单项选择题

The author states that birds left the tropics because （）

A．there was not enough food there in the winter
B．there were too many birds
C．there were too many glaciers
D．there was too much daylight

<上一题目录下一题>

热门试题

单项选择题According to one theory, when the glaciers disappeared, birds（）

A．stopped migrating
B．continued migrating
C．began migrating again
D．migrated south and stay there

单项选择题This passage supports the belief that（）

A．exact reasons for migration are not known
B．birds migrate because of changes in temperature
C．the ancestral home of all birds was the tropics
D．glaciers caused birds to migrate