现在完成时的所有知识,特别是短暂性动词与延续性动词,since 能不与短暂...答:for, since, so far, ever, never, just, yet, till / until, up to now, in past years, ...如:borrow改为keep/have;die改为be dead;leave改为be away等,或将完成时改为一般过去时 。 如: ...应改为:He has been on the Internet for six hours. 但须注意:终止性动词的否定式可以和since ...