题目内容：

Every year，millions of Monarch Butterflies(帝王蝶) fly 4,000 km from Canada     Mexico and then 4,000   again. They stay in Mexico for over six months, from October to April,   it is cold in Canada during(在…期间) that time. In Mexico, they lay eggs(产卵) and then die(死亡). In    , the new butterflies start to fly back to . There, they die they lay eggs. Then the   butterflies fly to Mexico again. Monarch Butterflies always go to the same places in Mexico and to the   trees. How do they know the   ?   do they go to the same trees? Only Monarch Butterflies know.

1.A. by       B. in       C. to        D. over

2.A. there      B. back      C. straight       D. across

3.A. if      B. because     C. but      D. and

4.A. April        B. October      C. November     D. winter

5.A. the UK      B. the USA      C. Canada       D. China

6.A. before      B. after       C. behind      D. later

7.A. strong      B. weak      C. new       D. old

8.A. same       B. different      C. tall      D. young

9.A. path       B. road       C. way       D. Mexico

10.A. How long   B. Why   C. How often           D. What