1 . During the holidays, many people hang mistletoe (槲寄生) over doorways. People share kisses under this evergreen plant. It is a popular Christmas tradition. But don’t let the image of romantic plant used during the happy times of the holidays fool you. In the forests they’re from, mistletoe plants can do some real damage. Let’s take a look at how and why.
The mistletoe plant is evergreen. This means it has leaves that remain green throughout the year. It is also poisonous and has white berries (浆果) and small, yellow flowers. The mistletoe lives on other plants, taking water and nutrients from them. For this reason, mistletoe plants are considered parasites (寄生植物).
The white berries of mistletoe plants contain seeds. Some birds and mammals like to feed on these berries. When they do, the seeds may stick to the animal eating the berries. The animal may carry the seeds to another part of the tree of bush. They may also carry the seeds to another plant altogether. The seeds start to grow roots that dig through the bark of the tree or bush. The roots grow into the tissues of the plant they’ve taken over. That’s how mistletoe plants take nutrients and water away from the host plants. Mistletoe can be hard to remove once it infects (感染) a plant. The best way to fight off a mistletoe infection is to cut off the infected branch completely. If the mistletoe takes over more parts of the plant, it can start to weaken the plant and make it harder for it to grow.
As mistletoe plants grow in the trees, they become a thick mix of branches and roots. This big mass is sometimes called a “witch’s broom.” Some animals nest in these witches’ brooms.
1. What is the effect of the mistletoe on host plants?| A．It makes the plants turn green. |
| B．It makes the plants attacked by pests more frequently. |
| C．It affects the growth of the plants. |
| D．It stops the plants producing nutrients and water. |
| A．It provides water and nutrients for other plants. |
| B．It is a poisonous evergreen plant. |
| C．It stands for peace during the Christmas holidays. |
| D．It has some magic power like a witch’s broom. |
| A．An Unlikely Parasite: Mistletoe | B．A Widespread Plant: Mistletoe |
| C．A Witch’s Broom: Mistletoe | D．A Popular Gift: Mistletoe |
2 . People often recommend planting trees to make cities greener, cleaner and healthier. But during heat waves, city trees can actually increase air pollution. Indeed, a new study finds that up to 60% of the ozone (臭氧) in a city’s air on hot days may have its origin in chemicals released by trees.
City trees offer a host of benefits. They provide cooling shade, absorb carbon dioxide, and also release oxygen into the air. But oxygen is far from the only gas that trees and certain other green plants release into the air. One of these chemicals is a hydrocarbon(碳氢化合物) that can react with burning pollutants, such as nitrogen oxides (氮氧化合物). The result is the formation of ozone which can cause airway diseases.
Galina Churkina works in Germany at Humboldt University of Berlin. She and her team wanted to explore how much chemicals released by trees could affect city air. To do this, the researchers turned to a computer. They asked it to model the likely reactions between plant chemicals and nitrogen oxides in air throughout the Berlin city area. To do that, the researchers fed in local weather data for two summers. One was 2006, when there was a heat wave. The other was 2014, when temperatures were mild.
An average daily high there in summer tends to be at roughly 25℃. On such a day, chemicals released by area greenery would likely have contributed to making about 6 to 20 percent of the ozone in the city’s air. But during a heat wave, when temperatures are more than 30℃ , tree-chemical emissions (发出物) are also high. As a result, they are now likely to be responsible for up to 60 percent of the ozone in air.
Churkina says her team was not surprised to see the contrary relationship between plants and pollution. The results, Churkina says, suggest city tree-planting programs should not ignore the role this greenery may play in bad summer air pollution. Adding more trees will improve quality of life only if those cities also undertake plans to sharply cut vehicle pollution (汽车污染).
1. What might people think of the new study finding?| A．Reasonable. | B．Intelligent. | C．Surprising. | D．Disappointing. |
| A．It is released by trees and other green plants. |
| B．It directly comes from the burning of oxygen. |
| C．A part of nitrogen oxides results in ozone in the end. |
| D．It is from the chemical reaction between a hydrocarbon and burning pollutants. |
| A．The higher the temperature is, the more ozone forms. |
| B．There’re no emissions of chemicals in spring or autumn. |
| C．Churkina suggests the number of city trees be lessened. |
| D．Churkina was surprised at seeing the contrary finding first. |
3 . The huge billboard at the side of the highway is no joke; transporting firewood in certain areas is a crime, punishable by a four-thousand-dollar fine. The reason? Emerald Ash Borer disease, or EAB disease, a new addition to the long list of dangerous foreign pest infestations（虫害）on American soil. It was in 2002 when the Emerald Ash Borer beetle（甲虫）was first discovered in Michigan. Not long after, the pest was found in Ohio. Originally from Asia, this green beetle probably found its way to North America through a wooden box made of ash wood and immediately settled into a local ash tree. In little time, the species managed to kill millions of ash trees.
To date, much work is underway to stop ash trees ending up in the same group as elm and chestnut trees, which are all dying out in many areas. Ash Borer Infestations are particularly troublesome because they are difficult to identify until the ash tree is heavily infested. In addition, other ash trees in the area surrounding the source will probably also be infested, making control a hard task.
Researchers are working on many issues related to the control and removal of this harmful beetle. For example, it has been discovered that Asian ash trees are not destroyed by this native borer. It may be that, Asian ash trees have developed genes（基因）to protect them from the insect; therein, perhaps, lies the secret to controlling this pest. Insecticide（杀虫剂）treatment is also being explored on several fronts. Research is underway to determine which insecticides are proving to be the most successful. The proper application of the insecticides is being debated.
However, all possible solutions require a great deal of study and research. In the meantime, careful steps must be taken. Methodical identification of infested trees is taking place. Identified trees are being cut down and destroyed to get rid of the beetle colonies（群）. In the end, this puts a huge drain（消耗）on city budgets, as tree removal can be extremely expensive.
Even though it will be expensive to deal with this problem in the short term, the costs of doing nothing could be far higher, since we could lose an entire species of tree.
1. What can we learn about the Emerald Ash Borer beetle?| A．It is a newly found species. |
| B．It can be used to fight foreign pest infestations. |
| C．It is native to North America. |
| D．It can cause damaging harm to American ash trees. |
| A．They affect Asian ash trees most frequently. |
| B．They are difficult to identify and get rid of. |
| C．They break out at certain times every year. |
| D．They spread slowly in a small area. |
| A．Gene activation. | B．Insecticide use. |
| C．Removing infested trees. | D．Introducing the beetle’s enemies. |
| A．Healthy trees should be relocated and protected. |
| B．Protecting the ash tree should be done at any cost. |
| C．Government budget for tree removal should be cut. |
| D．Measures that have side effects should be avoided. |
4 . Burning coal for energy adds planet-warming carbon dioxide(CO2) to Earth's atmosphere. As the planet heats up, experts warn that simply cutting greenhouse gas emissions（排放） will not be enough to avoid global warming. CO2 must also be remcved from the atmosphere.
Existing experimental machines that pull CO2 directly from the air are too expensive to be widely used. But a new effective technology to remove CO2 already exists. It is not expensive and easy. It is forests. Planting trees and watching forests are effective ways to clean the air.
Forests used to cover large areas of the Appalachian Mountains in the eastern United States. In the state of West Virginia, coal mining left the land there bare, without trees. Over the years, coal mining and cutting forests took over 90 percent of the red spruce（云杉） forests.
Chris Barton works for the University of Kentucky. He started a group called Green Forests Work, aiming to put trees back on the roughly 400 , 000 hectares of land.
However, Barton explains the land has problems. "If you planted trees on these places, they just didn't grow. The ground was too hard. Water didn't infiltrate（渗透）. The trees can't root. Oxygen can't circulate in those environments. "Using heavy equipment, workers tear the ground. In this way, the trees put down roots.
Barton says not everyone believes the solution is a good idea. "We've had a lot of doubtful look at us twice from people. But after we do it, there's no question that it was the right thing to do. "And it has worked. Forests are coming back to the grounds.
Scientists say that, in West Virginia alone, restoring red spruce forests to the area could send what is equal to 56 million barrels（桶）of oil into the ground. But it will take time—a long time. Around the world, experts say, nature offers powerful tools to fight climate change. But patience is needed. Nature works, but slowly, in its own time.
1. What is the economical and effective way to remove CO2 from the air?| A．Inventing new and powerful machines. | B．Cutting greenhouse gas emissions. | C．Making use of natural gases instead of coal. | D．Planting trees and protecting forests. |
| A．Cry. | B．Repair. | C．Destroy. | D．Cover. |
| A．oxygen is not enough for trees to grow there |
| B．too many rocks had made it hard to plant trees |
| C．coal mining has spoiled the land through years |
| D．there is no water for trees to grow there |
| A．a painful process | B．a slow process | C．a creative process | D．a learning process |
