標(biāo)志詞：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動(dòng)詞、助動(dòng)詞、情態(tài)動(dòng)詞之后，實(shí)意動(dòng)詞之前）常與yet進(jìn)行轉(zhuǎn)換。例如：I have already finished the work.我已經(jīng)完成這項(xiàng)工作了。 改為否定句：I haven't finished the work yet.我還沒(méi)有完成這項(xiàng)工作。改為一般疑問(wèn)句：Have you finished the work yet?

yet

放在否定句和一般疑問(wèn)句句末。

其他的標(biāo)志詞: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（多用于一般過(guò)去時(shí)），up to present，so far，up to now，up till now，till now。

since+時(shí)間點(diǎn)=for+時(shí)間段=since+時(shí)間段+ago

since+一般過(guò)去時(shí)態(tài)的時(shí)間狀語(yǔ)從句。例如：He has been here since he joined the army。自從他參軍以來(lái),他一直在這兒。

before

表示之前發(fā)生的事情，放在句末

例如：I have been to this place before.我之前去過(guò)了這個(gè)地方

just

表示剛剛做過(guò)的事情，放在have/has后面

例句：I have just cleaned my room.我剛剛清理了我的房間

ever

表示經(jīng)常的或習(xí)慣性的動(dòng)作，常與表示頻率的時(shí)間狀語(yǔ)連用。放在have/has后面，動(dòng)詞后面

例句：Their debts have grown ever larger。他們的債務(wù)不斷增加。

肯定句：

He/she/it+has+過(guò)去分詞

You/We/They+have+過(guò)去分詞

否定句：

He/she/it+hasn't+過(guò)去分詞

You/We/They+haven't+過(guò)去分詞

疑問(wèn)句：

Have/has+主語(yǔ)+過(guò)去分詞？