AIDS is said to( have been)the biggest challenge to human ov

来源：学生作业帮编辑：作业帮分类：英语作业时间：2024/05/10 05:42:31

AIDS is said to( have been)the biggest challenge to human over the past few year
括号中的have been,语法书上说用完成时是指过去发生的事情,并且对现在有影响时才用,这句里的AIDS不是在上几年才发生的吗?对现在还有影响吗.那么,请问什么时候用完成,什么时候用过去时呢/

你想想艾滋病现在还在肆虐,一直就在影响我们,怎么肯能会没有影响呢
所以这里用have been是对的
用过去时表示过去某个时间里发生的动作或状态,就在那个时间段里有影响
比如 I played basketball yesterday.我昨天打了篮球.这是昨天的事,不关现在的事了,对我没影响了.

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