Driving an electric car     1     to the protection of environment, or so the marketing departments of their makers would have you believe. Yet a report which analyzes car emissions presents a rather different picture. A battery-powered car recharged with     2     generated by coal-fired power stations, it found, is likely to be more harmful. It could cause more than three times as many deaths from pollution as a     3     petrol-driven vehicle.

The study was carried out by the University of Minnesota. The researchers estimated how levels of fine particulate matter (细颗粒物) and ground-level ozone — two important     4     of air pollution — would change when a car is powered by different ways.

It was no surprise that electric cars whose batteries were recharged with power from wind, solar or hydro-electric sources came out to be virtually free from harmful     5    . They were estimated to cause 231 deaths over the course of a year, compared with 878 for petrol cars. Electric cars recharged with power from natural gas-fired stations were also a lot less harmful than petrol-driven ones, with 439 deaths. But if those same electric cars were recharged     6     by coal, they would be responsible for over 3,000 deaths.

Biofuels also caused more health problems than petrol. But diesel, which often     7     concern about pollution, is slightly cleaner than petrol. This is because the study assumes for all cars that emission-control technologies will be more widely used, especially particulate filters which have a remarkable effect on cleaning diesel     8    . Diesel cars are also more     9     of fuel than petrol-driven ones.

Overall, the study shows that electric cars are cleaner than those traditional vehicles only if the power used to charge then is also clean. That is hardly a surprise, but the     10     of the difference is. How green electric cars really are, then, will depend mainly on where they are driven. In France, which obtains more than half of its power from nuclear station, electric cars look like a good bet. In China and some other developing countries, where a large amount of electricity is produced from coal, they may not be so environment- friendly as they are marketed.

Aunt Em dropped her work and came to the door. One glance told her of the danger close at hand. “Quick, Dorothy!” she screamed. “Run for the cellar!” Toto jumped out of Dorothy’s arms and hid under the bed, and the girl started to get him. Aunt Em, badly frightened, threw open the trap door in the floor and climbed down the ladder into the small, dark hole. Dorothy caught Toto at last and started to follow her aunt. When she was halfway across the room there came a great roar from the wind, and the house shook so hard that she lost her footing and sat down suddenly upon the floor.

Then a strange thing happened. The house circled around two or three times and rose slowly through the air. Dorothy felt as if she were going up in a balloon. It was very dark, and the wind blew horribly around her, but Dorothy found she was riding quite easily. After the first few twists and turns, and one other time when the house tipped badly, she felt as if she were being rocked gently, like a baby in a cradle (摇篮). Toto did not like it. He ran about the room, now here, now there, barking loudly; but Dorothy sat quite still on the floor and waited to see what would happen.

At last she crawled over the swinging floor to her bed, and lay down upon it; and Toto followed and lay down beside her. In spite of the swinging of the house and the crying of the wind, Dorothy soon closed her eyes and fell fast asleep.

Green Spring Renews Life’s Promise

For me, two of the loveliest words in the English language are “Life persists”. I came across them years ago as a college freshman, sitting in the library on a beautiful spring day, bored, working on a history paper. I don’t recall     1     I was researching into. Out of nowhere, those two words came     2     (dance) off the page in a quote by Gandhi, “In the midst of death life persists, in the midst of untruth truth persists, in the midst of darkness light persists.”

After those words     3     (read) again a dozen times, suddenly I was no longer bored. Outside in the sunshine, I kicked off my shoes and danced barefoot across a spring-green lawn.

I love spring. And this year, I was especially hungry to see it. Flying home last weekend to Las Vegas, after 10 days in California, I looked down on hills that were so green that I     4     almost taste them. When I approached Vegas, the green turned a dull desert brown. We landed after sunset, and the only green to be seen was neon(霓虹灯).

But the next morning, to my surprise, I     5     (awake) to find signs of spring all over my yard.     6     my absence, all sorts of things had leafed and bloomed. Three days later, I drove to Arizona to visit a friend and get yet another taste of spring seeing the Giants play the A’s in spring training. The drive across the desert was completely great, a variety of wildflowers and blooming cactuses.

Sometimes we need the chance     7     (remind) that we’re still alive. After my husband died, a friend sent me a card which read: “Just     8     you think you will never smile again, life comes back.”

Life persists, and so do     9     in the green of spring and the dead of winter, in the birth of a child and the passing of a loved one; in the words we leave behind and the hearts of those     10     will remember us. Spring reminds us that we’re alive forever.

6 . Being able to land safely is a critically important skill for all flying animals. Whereas terrestrial animals face no particular challenge when they need to stop running or crawling, flying animals move at much higher speeds, and they must be careful about how they land. Hitting the ground, or even water, at full flight speed would be quite dangerous. Before touching down, they must decrease their speed in order to land safely. Both bats and birds have mastered the skill of landing, but these two types of flyers go about it quite differently.

In the past it was believed that, in terms of flying mechanics, there was little difference between bats and birds. This belief was based only on assumption, however, because for years nobody had actually studied in detail how bats move their wings. In recent years, though, researchers have discovered a number of interesting facts about bat flight. Bats are built differently from birds, and their wings incorporate(结合) both their front and hind limbs (后肢). This makes their limbs working together more difficult for bats and, as a result, they are not very good at flying over longer distances. However, a bat can quickly change its direction of flight or completely reverse it, something a bird cannot easily do.

Another interesting characteristic of bat flight is the way in which bats land—upside down! Unlike birds, which touch down on the ground or on tree branches, bats can be observed flying around and then suddenly hanging upside down from an object overhead. How do they do it? A group of researchers recently used video cameras to film bats landing on nets suspended from the ceiling of their laboratory and studied the recordings in slow motion. They painted spots on the bats’ wings to see in detail what happens to the wings in flight and during touchdown. It turns out that the bats flew in a straight line up to the net and then quickly flipped over and attached themselves to it upside down. One disadvantage to this landing routine is that the bats often slam into their landing spot with some force, which probably causes pain. However, not all bats hit their landing spots with the same speed and force; these will vary depending on the area where a bat species makes its home. For example, a cave bat, which regularly rests on a hard stone ceiling, is more careful about its landing preparation than a bat more accustomed to landing in leafy treetops.

Can Indoor Plants Really Purify the Air?

Plants are very important to human life. Through photosynthesis (光合作用), they transform carbon dioxide into fresh oxygen. They     1    (assume) to remove toxins from the air we breathe—but is this true?

One famous NASA experiment, published in 1989, has found indoor plants can clean the air by removing pollutants     2    (cause) cancer. Later research has found soil micro-organisms in the potted plant also     3    (play) a part in cleaning indoor air.

Based on this research, some scientists say house plants are effective natural air purifiers, and the bigger and leafier the plant, the better. The amount of leaf surface area influences the rate of air purification.     4    , however, say the evidence that plants can effectively accomplish this feat (功绩) is far from conclusive.

“There are no definitive studies to show that having indoor plants can significantly increase the air quality in your home,”     5    Luz Claudio, a professor of environmental medicine and public health. “There’s no question     6    plants are capable of removing volatile (易挥发的) chemical toxins from the air under laboratory conditions,” says Claudio. But in your home or office space, the notion that putting a few plants together can purify your air doesn’t have much hard science     7    (back) it up.

Most research efforts to date, including the NASA study, placed indoor plants in small,     8    (seal) environments to assess how much air-purifying power they have. “But those studies aren’t really applicable to what happens in a house. In many cases, the air in your home completely turns over—that is, exchanges places with outdoor air—once every hour. In most instances, air exchange with the outside has a     9    (great) effect on indoor air quality than plants.” says Stanley Kays, a professor of horticulture (园艺学).

Disappointed     10    many people may be by what Kays said, the professor also made it clear that he believes house plants are beneficial. Studies have shown plants can knock out stress and make people feel happier. More research shows spending time around nature has a positive effect on a person’s mood and energy levels.