托福（TOEFL）考试阅读模拟试题（7）内容简介
托福（TOEFL）考试阅读模拟试题（7）
Questions 1l-20
According to some scientists, migratory birds should be able to wIThstand the winter.
A bird s feathery cOAt is good insulation against the cold. BECause a bird is warm- blooded, its body temperature always remains constant, even if the temperature of ITs surroundings changes.
The factors that trigger migratory behavior in birds are difficult to explain. This behavior seems to be instinctive, not learned. For example, many northern species leave their summer homes while the weather is still warm and the food supply plentiful. Young arctic terns born at the arctic breeding grounds will lake off wITh the flock for distant lands they have never seen.
bird migrations are probably regulated by the gland
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