since和for的两人外句子

现在完成时常和since引导的短语或从句，或由for引导的表一段时间的短语连用。

第一句是对的。for接一段时间，since接一个时间点。
因此第二句He has been dead since three years.应该在后面加上ago，表示一个时间点。
第三句应该是现在完成时，It has been three years since he died.

1.He has been dead for three years. （正确）
2.He has been dead since three years(ago).
= He was dead three years ago.
=He died three years ago.
3.It is three years since he died. （正确）
= It has been three years since he died.

第一句是对的。for接一段时间，since接一个时间点。
因此第二句He has been dead since three years.应该在后面加上ago，表示一个时间点。
第三句应该是现在完成时，It has been three years since he di

第二句错了， for后面跟时间段，since后面跟时间点

第三句也错了，since要用完成时，it has been three years since he died.

since引导时间点，for引导时间段

楼上说得对