Kramer发现被关在笼子里的侯鸟同往常去野外开始迁徙的时候变得焦躁不安。而且，他注意到，当这些鸟在笼子里焦躁不安时，它们通常会飞向迁徙路径的方向。于是，Kramer用星椋鸟做实验，将它们关在笼子里，总结出了它们的迁徙方向。事实上，它们基本都能朝向正确的迁徙方向，阴天除外。因为阴天的时候它们的焦躁不安使得它们难以清楚分辨方向。

根据本段话，候鸟在什么时候变得焦躁不安？

A.当天气乌云密布时

B.当他们没有辨别正常迁移途径时

C.当他们要开始迁移时

D.当用镜子改变太阳看起来所在方位时 

Paragraph 4:

The particular symbolic significance of the cave paintings in southwestern France is more explicitly revealed, perhaps, by the results of a study conducted by researchers Patricia Rice and Ann Paterson. The data they present suggest that the animals portrayed in the cave paintings were mostly the ones that the painters preferred for meat and for materials such as hides. For example, wild cattle (bovines) and horses are portrayed more often than we would expect by chance, probably because they were larger and heavier (meatier) than other animals in the environment. In addition, the paintings mostly portray animals that the painters may have feared the most because of their size, speed, natural weapons such as tusks and horns, and the unpredictability of their behavior. That is, mammoths, bovines, and horses are portrayed more often than deer and reindeer. Thus, the paintings are consistent with the idea that the art is related to the importance of hunting in the economy of Upper Paleolithic people. Consistent with this idea, according to the investigators, is the fact that the art of the cultural period that followed the Upper Paleolithic also seems to reflect how people got their food. But in that period, when getting food no longer depended on hunting large game animals (because they were becoming extinct), the art ceased to focus on portrayals of animals.

According to paragraph 4, which of the following may best represent the attitude of hunters toward deer and reindeer in the Upper Paleolithic period?

A. Hunters did not fear deer and reindeers as much as they did large game animals such as horses and mammoths.

B. Hunters were not interested in hunting deer and reindeer because of their size and speed.

C. Hunters preferred the meat and hides of deer and reindeer to those of other animals.

D. Hunters avoided deer and reindeer because of their natural weapons, such as horns.

Paragraph 4:

By 1800 more than a thousand steam engines were in use in the British Isles, and Britain retained a virtual monopoly on steam engine production until the 1830s. Steam power did not merely spin cotton and roll iron; early in the new century italso multiplied ten times over the amount of paper that a single worker could produce in a day. At the same time, operators of the first printing presses run by steam rather than by hand found it possible to produce a thousand pages in an hour rather than thirty. Steam also promised to eliminate a transportation problem not fully solved by either canal boats of turnpikes．Boats could carry heavy weights, but canals could not cross hilly terrain; turnpikes could cross the hills, but the roadbeds could not stand up under great weights. These problems needed still another solution, and the ingredients for it lay close at hand.  In some industrial regions, heavily laden wagons, with flanged wheels, were being hauled by horses along metal rails; and the stationary steam engine was puffing in the factory and mine．Another generation passed; before Inventors succeeded in combining these ingredients by putting the engine on wheels and the wheels on the rails, so as to provide a machine to take the place of the horse. Thus the railroad age sprang from what had already happened in the eighteenth century.

According to paragraph 4, which of the following statements about steam engines is true?

A. They were used for the production of paper but not for printing

B. By 1800, significant numbers of them were produced outside of Britain

C. They were used in factories before they were used to power trains

D. They were used in the construction of canals and turnpikes