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Scientists think they have answered a mystery: How some ocean creatures got so huge so quickly.

A few million years ago, the largest whales, averaged about 15 feet long. Then seemingly overnight, one type of whale, the toothless baleen whale（須鯨類）became huge. Modern blue whales get as big as 100 feet. Nicholas Pyenson of the Smithsonian Natural History Museum said, “Why is that?” ”It happened in the glance of an evolutionary eye, which makes it harder to figure out what happened,” said Graham Slater, lead author of the study. Their study has suggested an answer: Ice ages in the last 3 to 5 million years started it, changing the oceans and food supply for whales.

The researchers used fossil records of the smaller whales to create a family tree for baleen whales which include blue whales, humpbacks and right whales. Using computer simulations（模擬）and knowledge about how evolution works, they concluded that when the size changes started, the poles got colder, ice expanded and the water circulation in the oceans changed and winds shifted, Slater and Pyenson said cold water went deep and moved closer to the equator(赤道）and then eventually moved back up with small fish and other small animals that whales eat.

Baleen whale, which have no teeth, feed by eating huge amounts of fish they capture. Toothed whales, like sperm whales (抹香鯨), hunt individual fish, so the ocean chants that made food less evenly spread out didn’t affect them as much. But baleen whales hunt schools of fish.

Olivier Lambert at the Royal Belgian Institute of Natural Sciences calls it “a really convincing situation”. But he said the lack of fossils in certain time periods is an issue. As oceans warm from man-made climate change, the seas will be more like it was when the whales smaller and they will have a more difficult time surviving.

1.What does the author mean by “It happened in the glance of an evolutionary eye” in the second paragraph?

A. The change of baleen whales happened too quickly.

B. The change of baleen whales was too difficult to explore.

C. Researchers paid little attention to the change of baleen whales.

D. Researchers thought the change of baleen whales was unimportant.

2.What played the key role in baleen whales’ becoming huge?

A. Man-made climate change.

B. Its eating a huge amount of fish.

C. The water circulation in the oceans.

D. The increase of food supply for whales.

3.What do we know about sperm whales and blue whales according to the text?

A. Sperm whales eat more food.

B. Blue whaler live much longer.

C. Sperm whales prefer to hunt schools of fish.

D. Blue whales usually swallow schools of fish.

4.What can we infer from the last paragraph?

A. There are no whale fossils now.

B. The whales may become even bigger.

C. Global warming has threatened the whales.

D. Olivier Lamber thinks the study is perfect.

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