五、阅读理解
When autumn arrives in the United States and Canada, you can see one of nature's greatest scenes—the yearly migration(迁徙) of the monarch butterflies(帝王蝶).
No other butterfly in the world migrates(迁徙) like the orange and black monarchs of North America. They cannot live for long periods in cold weather. For this reason, each autumn around October, the butterflies from Canada travel up to 3,000 kilometres south to spend the winter in warmer locations. Some even fly to the mountains of Mexico. There are so many of them that they almost block out the sky. You can even hear their wings beating.
It usually takes the butterflies two months to reach the south of Mexico. After spending five months there, they head back north in the spring. They lay eggs along the way and die. Three generations of butterflies will live and die during the spring journey. The fourth and final generation of the year is born in early autumn and will reach the north. But the butterflies hardly get to rest before starting the long journey south again to Mexico.
The most amazing thing about these butterflies is that they return to the very same trees in Mexico that their great-great-grandparents used the winter before.
However, the population of this colourful butterfly has dropped in recent years. In 2015, the US Fish and Wildlife Service said that nearly a billion monarchs had disappeared from the overwintering sites(越冬地点) since 1990, reported the Washington Post. One of the main reasons, experts say, is that farmers have used herbicides(除草剂) on plants that the monarchs' larvae(幼虫) live and feed on.
()1. When do monarch butterflies travel south?
A. In autumn. B. In spring. C. In winter. D. In summer.
()2. Why do monarch butterflies fly to the south every autumn?
A. To find suitable places to lay eggs.
B. To avoid the strong winds in the north.
C. To look for a warmer place to live.
D. To look for new types of food sources.
()3. What can we know according to the passage?
A. The butterflies spend two months staying in the south of Mexico.
B. In the south, the butterflies will all stay on one tree.
C. The butterflies that fly back to the north are not the same ones that flew to the south.
D. The butterflies will get to rest before starting the long journey south again to Mexico.
()4. What is the main idea of the passage?
A. The harm of farm herbicides to monarch butterflies.
B. Special winter homes of monarch butterflies in Mexico.
C. The way monarch butterflies finish their round-trip journey.
D. The migration of monarch butterflies and the dangers they face.

1. A 2. C 3. C 4. D