1.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?
2.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。
3.before
表示之前发生的事情，放在句末
例：I have been to this place before.我之前去过了这个地方
4.just
表示刚刚做过的事情，放在have/has后面
例：I have just cleaned my room.我刚刚清理了我的房间
5.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：Their debts have grown ever larger。他们的债务不断增加。
