如果甲产品对乙产品的需求交叉弹性系数是负数，则说明甲产品和乙产品（）。

A.无关

B.是替代品

C.是互补品

D.是缺乏价格弹性的

(2013·湖南高考)He ________ sleep, although he tried to, when he got on such a hunt for an idea until he had caught it.

A．wouldn't

B．shouldn't

C．couldn't

D．mustn't