现在完成时；疑问句；
have是助动词.
现在完成时是英文时态的一种
现在完成时的用法
have(has)+过去分词(done)
1.现在完成时用来表示现在之前已发生过或完成的动作或状态,但其结果却和现在有联系,也就是说,动作或状态发生在过去但它的影响现在还存在.
I have lost my wallet.(含义是:现在我没有钱花了.)
Jane has laid the table.(含义是:已可以吃饭了.)
Michael has been ill.(含义是:现在仍然很虚弱)
He has returned from abroad.(含义是:现在已在此地)
2.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.
3.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,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
4.现在完成时常常与表示频度的时间状语连用,如often,sometimes,ever,never,twice,on several occasion等:
Have you ever been to Beijing
I have never heard Bunny say anything against her.
I have used this pen only three times.It is still good.
George has met that gentleman on several occasions.
5.现在完成时还往往可以同包括现在时间在内的时间状语连用,如now,up to these few days/weeks/months/years,this morning/week/month/year,now,just,today,up to present,so far等:
Peter has written six papers so far.
Man has now learned to release energy from the nucleus of the atom.
There has bee too much rain in San Francisco this year.
The friendly relations and cooperation between our two countries have been enhanced in the past few years.
Up to the present everything has been successful.
6.现在完成时表示现在之前业已完成的动作,虽然其效果或影响仍然存在但已不再继续,但是有一些现在完成时的句子,在后面加上for+一段时间,则现在完成时的动作就表示延续性.
Thomas has studied Russian.(现在不再学俄语)
Thomas has studied Russian for three years.(=Thomas began to study Russian three years ago,and is still studying it now.(同第2点用法第一个例句)
7.现在完成时还可以用来表示过去的一个时间到现在这段时间内重复发生的动作.
We have had four texts this semester.