Human beings act in a different way from 21______ of animals just because they can speak while animals cannot. Even the cleverest animals cannot do things which to us seem very 22______ and which small children, as soon as they learn to talk, would be able to do.
A German scientist, who 23______ experiments for many years with big apes, found that his apes could use his sticks as tools to pull down bananas which they could not 24______. But they only used the stick to get a banana when both the banana and the stick were in view at the same time. If the banana was in front of them and the stick was behind them, they could not use the stick. They could not keep the banana 25______ enough in mind to look around and then pick up the stick and use it.
The 26______ for this is clear. We have words for banana and stick which help use to think about these things when they are not in 27______. Even a small child knowing the words “banana” and “stick” has an idea of their relationship and is able to think “stick” together with “banana” and to remember this long enough to pick the stick 28______ behind and use it on the banana.
29______ to speak, animals cannot keep their knowledge of things for long. That is why they often interrupt one line of action to do something else and later forget it completely. Human beings, on the other hand, use 30______ and are able to do one thing continuously.
21.
A.that B.this C.way D.eat正确答案A
