2 . Humans have sailed the oceans’ surfaces for thousands of years, but their depths remain effectively uncharted. Only about a quarter of the seafloor has been mapped at high resolution (清晰度). Maps of most regions display only estimated depths and often miss entire underwater mountains or canyons (峡谷). So a group of researchers have turned to some deep-diving experts: Elephant Seals and Weddell Seals. Scientists have been placing trackers on these blubber y marine mammals around Antarctica for years, gathering data on ocean temperature and salinity (盐度).

For a new study, the researchers compared these dives’ location and depth data with some of the less detailed seafloor maps. They spotted places where the seals dove deeper than should have been possible according to the maps.

In eastern Antarctica’s Vincennes Bay, the diving seals helped the scientists find a large, hidden underwater canyon suddenly descending (下降) to depths of more than a mile. “The seals discovered the canyon, and the ship confirmed it,” says Clive McMahon, a researcher at the Integrated Marine Observing System in Australia and a co-author of the new study.

But seals can’t map the entire ocean floor. The trackers used in the study could pinpoint (为……准确定位) a seal’s geographical location only within about 1.5 miles, which allows for useful but not exactly high-resolution data. Plus, because the seals don’t always dive to the bottom of the ocean, they can reveal only where the bottom is deeper than in existing maps — not shallower. McMahon notes that scientists could improve on these data by using more precise GPS trackers and analyzing the seals’ diving patterns to determine whether they have reached the seafloor or simply stopped descending.

The current seal-dive data can still be valuable for an important task, says Anna Wåhlin, an oceanographer at the University of Gothenburg in Sweden. The deep ocean around Antarctica is warmer than the extremely cold waters at the surface, and seafloor canyons can allow that warmer water to flow to the ice along the continent’s coast, Wåhlin explains. To predict how Antarctica’s ice will melt, scientists will need to know where those canyons are and how deep they go.

4 . Between 20 and 40 per cent of planet Earth is covered in grasslands, across every continent except for Antarctica. Grass is a low-growing, flowering plant with groups of narrow leaves growing from its base. Strong roots typically hold this plant’s leaves firmly to the ground.

One of the most common sights along stretches of grass is grass-eating animals. This is because many large animals rely on extensive grasslands to survive, and grass grows well with this regular trimming (修剪). The plants gain their energy from sunlight and require healthy cells to do so. If the leaves aren’t cut, the tips die and start to rot. When they are damaged with a clean cut, however, the cells are caused to grow quicker and produce new, healthy tissue. This is also why cutting your garden’s grassland regularly can make your grass look thicker and healthier.

Humans rely on grass for food, too. Many grasses, such as w heat or corn, are harvested as a main part of some diets. Meanwhile, grass is used indirectly to produce food in the form of livestock (牲畜). Cattle farmers require grass in their fields to feed cows and sheep before they are turned into meat for human consumption.

One of the most debated questions is how long ago grass evolved. Because grass doesn’t preserve well as a fossil, a definitive answer is hard to come by. Until recently, many scientists estimated that grass began to grow on Earth between 50 and 65 million years ago.

However, within the last decade, a piece of 100-million-year-old amber (琥珀) was found that appeared to contain the oldest grass fossil to date. Studies of fossilized dinosaur faces (粪便) also suggest that some dinosaurs lived at the same time that grass grew on the planet, incorporating it into their diets.

Liulichang Cultural Street is known throughout China and the world for its ancient books, calligraphy, paintings, rubbings, ink stones and ink. The street, which is only 750 meters long,     1     (locate) south of Hepingmen Gate within walking distance of the Hepingmen Ouanjude Peking Duck Restaurant. It is     2     must-see for visitors traveling in Beijing.

Liulichang’s history can be traced back to the Tang Dynasty,     3     it was part of Jixian County. During the Liao Dynasty, it was known     4     Haiwangcun (Village of the Sea King). The kiln (窑) which made glazed tiles (琉璃瓦) was first built in the Yuan Dynasty. When Ming rulers began to build     5     (they) palaces in Beijing, the kiln was enlarged. Most glazed structural     6     (component) of the Ming halls and palaces were produced in the kiln. In Ming and Qing times , Liulichang was a favorite place for scholars, painters and calligraphers who gathered there     7     (write) and read books, as well as to paint and compose poetry.

In 1979, the Chinese government     8     (approve) a recommendation to restore and expand Liulichang. The     9     (origin) shops have been restored and the road broadened into a 15-meter-wide pedestrian mall. A museum     10     (display)classical paintings, calligraphy and other antiquities tells the story of the old street.

6 . Cruise through many neighborhoods or parks around the world, and you will find no shortage of well-mowed expanses of grass. Lawns (草坪) do look attractive.     1     Additionally, they can require environmentally questionable practices to maintain. Researchers and landscape architects are increasingly considering alternatives that are more sustainable, demand fewer resources and help people connect more intimately with nature. Here follows an edited excerpt of the conversation between researchers MariaIgnatieva and Marcus Hedblom.

Why did lawns become so popular?

    2     They were like a special frontier that separated cities and towns from the wilderness. A lawn was always a symbol of how a civilized society should be. That’s why it was so powerful. And of course, they are also important for recreation.

What environmental problems are lawns causing?

Lawns are homogenizing the environment, not only in terms of biodiversity but also visually. You compare countries’ and cities’ urban landscapes around the world, and they look exactly the same.     3    Mowers burn fossil fuels and emit gases that heat up the atmosphere.

    4       

You have to find your own local solution. We can take inspiration from the natural plant communities around us. In suburban and rural areas, that might mean having a meadow or prairie. In other places, it might be a savanna like environment or mountain plants. You can have a “grass-free” lawn; with only low-growing plants that create the same effect as a lawn, and you can walk on it.

How can we persuade people to adopt these alternatives?

When people see them, they appreciate them and like them.     5     We also have to try to change the minds of decision makers, including politicians. We need to show the public there are different ways of handling our urban environment and making it better.