第13题: [单项选择]The pressure ______causes Americans to be energetic, but it also puts them under a constant emotional strain. A. to compete B. competing C. to be competed D. having competed 参考答案:A 答案解析:英语中有很多名词可以接不定式作定语,pressure 就是其中之一,常用的还有ambition,campaign,chance, courage,decision,determination,driv