单项选择
6.he said he ________ a cold for a week. a.had had b.had caught c.has had d.has caught
选A。 从“for a week”可以看出,应该用完成时态。 而句子前面说 “he said ”,所以应该主谓一致,动词用had
答:6.d. had had 注意动词要用延续性动词 7.d. was, playing football 过去进行时 8.c. had left, arrive...详情>>
问:已知a,b属于R,求证:a^2+b^2>=a*b+a+b-1
答:答案如下: 由(a-1)^2+(b-1)^2>=0 得到a^2+b^2+2>=2(a+b)--------(1) 又由(a+1)^2+(b+1)^2>=2(a+...详情>>
问:“ prefer to...rather than ”是一个词组吗?
答:prefer to do rather than do sth 与其作后者的事情的不如做前者去事情。 可以等同于= prefer to do instead o...详情>>