have是什么时态的标志

现在完成时可以用来表示发生在过去某一时刻的`,持续到现在的情况,常与for,since连用.

Mary has been ill for three days.

I have lived here since 1998.

现在完成时往往同表示不确定的过去时间状语连用,如already, yet, just, before, recently,still, lately等:

He has already obtained a scholarship.

I haven't seen much of him recently (lately).

We have seen that film before.

Have they found the missing child yet