三句口訣：“主現(xiàn)從任、主過從過、主將從現(xiàn).”
意思是說：
主句是現(xiàn)在時的話,從句隨便你用什么時態(tài).
比如：I‘ll tell her the good news when she comes back.
Don’t laugh at me when I make a mistake.(祈使句)
You should be quiet when you are in the library.(含情態(tài)動詞)
主句是過去式的話,從句用四種過去時態(tài)中的一種（過去一般、過去進(jìn)行、過去完成、過去將來）
比如：When he entered the room,I stopped eating.
When he entered the room,I was eating.
When he entered the room,I had been eating for five minuted.
When he entered the room,I would have finished eating.這個不太恰當(dāng),但你能理解就行.
主句是將來時的話,從句用現(xiàn)在時.
I will be a nurse when I grow up.
 
另外,since 引導(dǎo)時間狀語從句時,其主句通常要用現(xiàn)在完成時,有時也用現(xiàn)在完成進(jìn)行時.如：
She has had another baby since I saw her last.從上次我見到她以來,她又生了一個孩子.
He has grown an inch since I saw him.我上次見到他以后他已長高了一英寸.
注：當(dāng)主句為“It + be + 一段時間”時,則通常用一般現(xiàn)在時代替現(xiàn)在完成時.如：
It’s more than three years now since I saw her last.我們已有三年多沒見面了.
 
一些特定句式的時態(tài)：
由no sooner...than,hardly [scarcely]…when引出的時間狀語從句,其主句通常用過去完成時,從句通常用一般過去時.如：
Hardly had he arrived when she started complaining.他剛到她就抱怨起來.
No sooner had he gone to sleep than the telephone rang.他剛睡著電話鈴就響了.
We had no sooner set out than a thunderstorm broke.我們剛出發(fā)就下起一陣?yán)妆?
No sooner had she agreed to marry him than she started to have terrible doubts.她剛同意嫁給他她就開始產(chǎn)生可怕的疑慮.
When you have finished your homework,I will give you 10 dollars.做完作業(yè),我給你十美元作為獎勵.
When he has come back,I have finished my homework.你到家的時候,我肯定已經(jīng)完成家庭作業(yè)了.
 
不懂問我,南無地藏菩薩!