题目内容：

    Every year, hundreds of millions of Monarch Butterflies (黑脉金斑蝶) from Canada and the United States journey as far as 2, 500 miles to the forests of Michoacan, Mexico, a place which has the world’s largest insect migration. It’s such a breathtaking sight, but as always, human greed is threatening to destroy it.

The Monarch Butterflies start to arrive in Michoacan in late October to make their winter home in the trees high up in the mountains of the natural reserve. Once there, they gather together in large masses. These masses often become so heavy that they cause tree branches to bend or even break. But there’s a purpose of all these massing - it allows the butterflies to survive in the low nighttime temperatures at these high altitudes.

The Michoacan Monarch Butterfly Sanctuary (保护区) is most impressive during the months of February and March, just before the winged insects begin their long journey home.

Mexico’s Butterfly Forest is a shelter protected by law, and one of the country’s most popular sights, but that hasn’t stopped people from slowly but steadily destroying it.

Illegal woodcutting in the heart of the Monarch Butterfly Biosphere Reserve has been a longstanding problem, but criminals are rarely brought to justice. They are often set free after paying some money.

Just last month, an even greater threat rose in Michoacan’s butterfly home. The country’s largest mining corporation gained the right to reopen an old mine in the heart of the monarch reserve. Experts believe that if the mine is reopened, it will likely spell the end of this magical place.

And as if all this wasn’t bad enough, the increasing use of herbicides (除草剂) in the American corn belt has led to the decrease of a plant which is essential to the monarchs’ development from egg into butterfly.

1.When do the Monarch Butterflies begin to fly back to Canada?

A.In January. B.After March. C.In October. D.In December.

2.What does the underlined word “it” in Paragraph 2 refer to?

A.The weather. B.The reserve. C.The massing. D.The forest.

3.What can we know about the protection of Monarch Butterflies in Mexico?

A.It is very satisfying.

B.It should be strengthened.

C.It cost the government a lot.

D.It has saved many butterflies.

4.What can we infer from the last two paragraphs?

A.Monarch Butterflies have a worrying future.

B.America has many mines waiting for exploration.

C.Monarch Butterflies live in the centre of an old mine.

D.The use of herbicides will let Monarch Butterflies lay fewer eggs.