单选题 What effect does confinement have on clever animals, according to the text?

A、 They never stop trying to escape.
B、 They lose all their muscles.
C、 They become unhygienic.
D、 They may go mad.

【正确答案】 D

【答案解析】[分析] 推断题型。根据第三段第一句...such an originally highly intelligent and mentally alert animal has deteriorated, in confinement, into a crazy idiot,...(由于被关在笼中，原本很聪明机敏的动物变成了疯狂的傻瓜)推断可知。