以下例句:
I was sleeping when he was wathcing TV.（過(guò)去進(jìn)行式)
= When he was wathcing TV,I was sleeping.
Every day I read newspaper when I eat breakfast.（現(xiàn)在式）
= Every day when I eat brakfast,I usually read newspaper.
What do you have to do when you go to school?(現(xiàn)在or未來(lái)式皆可)

(1)since + 過(guò)去一個(gè)時(shí)間點(diǎn) (具體的年、月、日期、鐘點(diǎn)).
I have been here since 2002.
(2)since +一段時(shí)間+ ago
I have been here since six months ago.
(3)since +從句
I'm very sad since you left.
(4)It is +一段時(shí)間+ since從句
It is six months since I came here.
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while所接子句中的動(dòng)詞是進(jìn)行式or單純式,但需要是有持續(xù)性的動(dòng)作或狀態(tài)
例:While there is life,there is hope.(有生命就有希望)
>
對(duì)現(xiàn)在、將來(lái)不確實(shí)事情的推測(cè)or對(duì)現(xiàn)在的事實(shí)相反的假設(shè)or與過(guò)去事實(shí)相反的假設(shè)皆可;
if 后面所連接的子句,可放在句首也可放在句中,但若是放在句首,則和其后子句間要用逗號(hào)分開(kāi).
例:I won't go out if you come here tomorrow.
=If you come here tomorrow,I won't go out.