标志词:just,ever,never,yet,already,for,before,since,so far,recently,twice,still,till now,up to now,three times等。
already
用在肯定句中(be动词、助动词、情态动词之后,实意动词之前)常与yet进行转换。例如:I have already finished the work.我已经完成这项工作了。 改为否定句:I haven't finished the work yet.我还没有完成这项工作。改为一般疑问句:Have you finished the work yet?
yet
放在否定句和一般疑问句句末。
其他的标志词:just,before,recently,still,lately,never,ever,twice,on several occasions,in the past/last few days/weeks/months/years,(up to)these few days/weeks/months/years,this morning/week/month/year(多用于一般过去时),up to present,so far,up to now,up till now,till now。
since+时间点=for+时间段=since+时间段+ago
since+一般过去时态的时间状语从句。例如:He has been here since he joined the army。自从他参军以来,他一直在这儿。
before
表示之前发生的事情,放在句末
例如:I have been to this place before.我之前去过了这个地方
just
表示刚刚做过的事情,放在have/has后面
例句:I have just cleaned my room.我刚刚清理了我的房间
ever
表示经常的或习惯性的动作,常与表示频率的时间状语连用。放在have/has后面,动词后面
例句:Their debts have grown ever larger。他们的债务不断增加。
肯定句:
He/she/it+has+过去分词
You/We/They+have+过去分词
否定句:
He/she/it+hasn't+过去分词
You/We/They+haven't+过去分词
疑问句:
Have/has+主语+过去分词?