Question

    For a bird, to fly hundreds or thousands of miles each spring and fall is a difficult and dangerous journey, one that not all birds can survive. 1. There is more than one single reason for different birds to migrate(迁徙), but it all comes down to survival.

Birds are migrating for a meal.

For all birds, one of the main driving forces behind migration is food. If all birds were to stay in the same places year-round, food there would become not enough. 2. But as the food supplies decrease in the fall, they return to the southern areas.

3.

Over millions of years, birds have developed different migration patterns, times and destinations. This helps birds take advantage of a wide variety of suitable conditions to raise their young, which increases the survival chances of the young birds.

Birds are migrating because of climate changes.

Changes in climate can affect migration. Many birds leave the Arctic for example, when temperatures begin to fall. They need warmer habitats. Similarly, the hottest regions can be an unpleasant environment for raising young birds. 4.

Birds are migrating because of predators.

Habitats that have rich food sources also attract a greater number of predators who may kill birds. 5. Many birds even migrate to specialized habitats that are nearly inaccessible to predators, such as coastal cliffs or rocky offshore islands.

A.So why do birds migrate?

B.Birds are migrating for their young.

C.So how do young birds migrate?

D.Birds are migrating because of diseases.

E.It is beneficial to lay eggs further north in cooler areas.

F.Birds that migrate to different habitats can avoid being eaten by predators.

G.As food sources are rich in the north each spring, millions of birds migrate from south to those areas.

Answer

1.A

2.G

3.B

4.E

5.F

【解析】

本文为说明文。文章主要叙述了鸟类迁徙的几点原因：鸟类迁徙是为了觅食，为了养育幼鸟、气候原因及避免被捕食。

1.考查对上下文的理解及推理判断能力。本空格的上文可知，鸟在春天和秋天要迁徙，在迁徙过程中并非所有的鸟能生存下来。空后的内容说“鸟类迁徙原因不只一个”可知，此空格是指“鸟类为什么要迁徙？”。分析选项可知A项符合语境，故选A。

2.考查对上下文的理解及推理判断能力。本小题所在小标题为“鸟儿迁徙是为了觅食”。分析选项可知G项符合题意。结合空前的上句的内容“对所有鸟类来说，迁徙背后的主要驱动力之一是食物。如果所有的鸟一年到头都呆在同一个地方，那里的食物就会变得不足”。以及下句“但是随着秋季食物供应的减少，它们又回到了南部地区”句中的转折连词but及the fall，可知，与fall相反的是春季，以及“return to the southern areas”可知，每天春天北方的食物丰富，鸟儿从南方迁徙到北方。分析选项可知，G项符合语境，故选G。

3.考查对上下文的理解及推理判断能力。分析选项可知，本空格是本段的主旨。本段讲述的是鸟类的迁徙有很多的模式。其中鸟类利用各种各样的适宜条件来养育幼鸟，以此增加了幼鸟的生存机会，即为养育幼鸟而迁徙，分析选项可知，B项符合语境。故选B项。

4.考查对上下文的理解及推理判断能力。本空格前说气候影响鸟的迁徙。鸟类在气温下降时，鸟离开北极到温暖的地方栖息。同样的，最热的地方也不适宜饲养幼鸟。不太冷也不太热的地方即在较凉爽的地方产卵。分析选项可知E项符合语境，故选E。

5.考查对上下文的理解及推理判断能力。本空格所在的小标题为“鸟类因捕食者而迁徙”。分析选项可知F项（迁徙到不同栖息地的鸟类可以避免被捕食者吃掉）符合语境，在说明迁徙的原因。故选F。