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Lesson 28: The Study of Living Things
第28课 生物研究
Dr. Chip Taylor teaches biology at a university in the United States.
琪普·泰勒博士在美国的一所大学里教生物学。
He studies one kind of North American butterfly.
他研究一种北美蝴蝶。
Just like a migrating bird, this butterfly travels about 4 000 kilometres south in fall.
就像候鸟一样，在秋季这种蝴蝶飞往4000余公里外的南方。
Fantastic facts about the butterfly have been drawing Dr. Taylor's attention.
这种蝴蝶的奇妙迁徙，吸引了泰勒博士的关注。
In Mexico, the butterflies always return to the same small piece of forest,
在墨西哥，蝴蝶们总是返回同一片小森林，
which is only 20 kilometres wide.
这片森林宽仅有20公里。
Here, as many as 230 million butterflies spend the winter.
有多达2亿3千万只蝴蝶在这里过冬。
They can cover some trees almost completely.
它们几乎把一些树完全覆盖了。
The butterflies that return to the south are the great-great grandchildren of the butterflies that left for the north.
迁徙至南方的蝴蝶是这些动身前往北方的蝴蝶们的曾孙辈。
When they begin to travel north in spring, the females lay eggs.
春天当它们开始飞回北方时，雌性蝴蝶会产下卵。
They lay eggs on only one plant: milkweed.
它们只把卵产在马利筋这种植物上。
But in Mexico, people cut down the trees that the butterflies need to rest on because they want more land for farming.
但是，在墨西哥，人们砍伐了蝴蝶栖息的树木，因为人们需要更多的土地种植农作物。
In the United States and Canada, farmers use chemicals that kill milkweed.
在美国和加拿大，农场主们使用化学药品杀死马利筋。
This worries Dr. Taylor a lot.
这让泰勒博士很担忧。
Now things are improving. Mexico has begun to protect parts of its forests.
现在情况都得到了改善。墨西哥已经开始保护部分森林。
The United States and Canada have encouraged farmers to use less chemicals.
美国和加拿大鼓励农场主们少用化学药品。
Scientists still don't understand how the butterflies know when to fly south.
科学家们仍然不理解蝴蝶如何知晓什么时候该飞向南方。
If they are even a few days late, they will freeze.
如果它们晚些天（迁徙），他们就将挨冻。
And how do all the great-great grandchildren find the same forest in Mexico every year?
蝴蝶的曾孙们，每年是如何找到相同的森林的？
This is both puzzling and interesting for many scientists.
这些仍然困扰着、也吸引着很多的科学家。
There are many mysteries yet to be discovered by those interested in science. Would you like to study biology?
仍然有许多奥秘还有待那些对科学感兴趣的人去发现。你想要研究生物学吗？
