单选题 Humans have been interested in how birds fly since the dawn of history. And they have long been studying the flight of birds and trying to copy it. Not until the twentieth century did engineers fully understand the principles (原理) of flight that birds have already been using for millions of years.
Birds are adapted (适应) in their body structure, as no other living things, to live in the air. Their wings, tails, light and hollow (空的) bones, and internal air sacs (体内气囊) all help to this great ability. These adaptations make it possible for birds to seek out environments most favorable to their needs at different times of the year. This results in migration—the regular, seasonal movement of the whole population of birds from one geographic location (地点) to another.
Each year with great regularity most species (品种) of birds return to their summer homes, hoping to court (求偶), choose mates, build their small comfortable homes, and lay eggs, as well as bring up their young. In the late summer and fall they get their new feathers. And then they join with other birds of their kind in large and small flocks (群), feeding and storing up fat in their bodies. In this way, they are well prepared for the hardships of winter, whether they decide to remain in the cold northlands or make the strength-wasting journey to the south.

单选题 The main idea of this passage is that ______.

A. birds are built to fly
B. birds are built the same as other living things
C. birds need to migrate to survive (生存)
D. birds need to be told when to migrate

【正确答案】 A

【答案解析】[解析] 主旨题。题干意为“本文主要讲述了什么?”整篇文章主要讲的是鸟类有利于飞行的身体结构。所以本题的正确答案为A。本题也可用排除法来做。选项B的陈述是错的，可以排除；选项C只是文章的一个细节，可以排除；选项D文章没有提及也可以排除。

单选题 It can be inferred from the second paragraph that ______.

A. birds' migration is generally without purpose
B. birds' migration is only out of their habits
C. birds are able to look for situation favorable to their existence
D. most birds travel regularly for a change in their life pattern

【正确答案】 C

【答案解析】[解析] 推断题。题干意为“从文章中第二段可以推断出什么?”从文章第二段最后两句“...birds to seek out environments most favorable to their needs at different times of the year. This results in migration...”可知，鸟类可以通过迁徙寻找适于生存的环境。所以本题的正确答案为C。

单选题 Birds feed and store, fat in their bodies ______.

A. for use in bringing up their young
B. for use in winter
C. to be used when they return next summer
D. to be used on their way south

【正确答案】 B

【答案解析】[解析] 细节题。题干意为“鸟类觅食并在体内储存脂肪是为了______。”从文章最后一段最后一句话“In this way, they are well prepared for the hardships of winter, whether they decide to remain in the cold northlands or make the strength-wasting journey to the south.”可知，鸟类觅食并在体内储存脂肪是为了过冬，所以本题的正确答案为B。

单选题 Which of the following is implied by the passage?

A. Each individual bird has its own pattern of migration.
B. All birds fly south for the winter.
C. Different kinds of birds make up different flocks in their migration.
D. Different kinds of birds join together in their migration.

【正确答案】 C

【答案解析】[解析] 推断题。题干意为“从文章中可以推断出什么?”从文章最后一段倒数第二句话“And then they join with other birds of their kind in large and small flocks...”可推知，在迁徙的过程中，不同种类的鸟形成不同的群体，所以本题的正确答案为C。