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Monarch butterflies（黑脉金斑蝶）are a common summer sight in the northern United States and Canada . These large orange and black insects（昆虫）brighten parks and gardens as they fly lightly among the flowers . What makes monarchs particularly interesting is that they migrate（迁飞）—all the way to California or Mexico and back . They are thought to be the only insect that does this .

Every year in the late summer monarchs begin their journey to the south . Those heading for Mexico go first for the Louisiana-Mississippi area , then fly across the Gulf of Mexico into Texas . Once in Mexico , they settle themselves in one of about fifteen places in a mountain forest filled with fir trees . Each place provides a winter home for millions of monarchs . The butterflies are so many that they often cover entire trees . When spring comes , they begin their long journey north .

The question is often asked whether every butterfly makes the round-trip journey every year . And the answer is no . The average monarch lives about nine months . So one flying north might lay eggs in Louisiana and then die . The eggs of that generation may be found in Kentucky ; the eggs of the next generation may end up in Wisconsin or Michigan . The last generation of the season , about the fourth , will make their way back to Mexico and restart the journey .

Scientists learn about monarchs’ migration by catching and making marks on the insects . By recatching a monarch with such a mark and noticing where it came from , the next scientist can get to know things like the butterfly’s age and its routing（路线）.

1. One of the places where monarchs spend the winter is ________.

A. the Gulf of Mexico B. an area in Mississippi

C. a forest in Mexico D. a plain in Texas

2. The routing of monarchs’ migration can be learned ________.

A. by examining the marks made on them

B. by collecting their eggs in the mountains

C. by comparing their different ages

D. by counting the dead ones in the forests

3. What is the subject discussed in the passage ?

A. Migration of monarchs . B. Scientists’ interest in monarchs .

C. Winter home of monarchs . D. Life and death of monarchs .

答案：1. C 2. A 3. A

在北美和加拿大地区，黑脉金斑蝶在夏季十分常见。当这些明橙色和黑色相间的大昆虫在花朵间翩翩起舞的时候，使得公园和花坛都变得活跃起来。有趣的是黑脉金斑蝶的迁飞--总是往返于加利福尼亚或墨西哥。人们认为，只有这种昆虫才这样做。

每年的夏末黑脉金斑蝶开始它们向南迁飞。目标方向墨西哥，首先进入路易斯安那-密西西比河地区，然后它们穿过墨西哥湾进入得克萨斯。一旦进入墨西哥，它们便会在大约十五分之一的冷杉树林密集的大森林内安顿下来。每一片冷杉树林密集的地方会为成千上万的黑脉金斑蝶提供越冬的场所。蝴蝶数量多的时候，它们经常会遍布整片树林。当春季来临的时候，它们又开始向北迁飞。

经常有人问是否每只蝴蝶每年都这样反复的迁飞于两地。答案是不。黑脉金斑蝶的平均寿命是9个月。所以蝴蝶向北迁飞，有可能在路易斯安那产卵后便死掉了，也有可能在肯塔基州产卵；也有可能在威斯康星或密歇根州产卵。最后的繁殖季节，大概是第四次繁殖，它们将返回墨西哥开始新一程的迁飞。

科学家们为了研究黑脉金斑蝶的迁飞习性，通常将捕捉到的蝴蝶做上记号，然后通过捕捉这些标有记号的黑脉金斑蝶，来观察蝴蝶飞来的方向，科学家以此方法来对黑脉金斑蝶进行研究，如它们的年龄和飞行路线等。