1. If 引导的条件句---条件句
If I am better tomorrow, I will get up.
If I have a headache, I will take an aspirin.
If she finishes early, she will go home.
时由was/were -ing 分词构成。
I was writing.
We were writing.
What were you doing last night at seven o'clock?
Workers were building a dam last summer.
He was always changing his mind.
She was always coming back late.
I have (I've) played.
He has (He's) worked.
She's turned off the light.(灯在被关了，说话时刻仍然关着。）
She's already gone.
It's rained quite recently.
We have often been there.
I've seen the film three times a month.
Up till now we have planted over 24,000 fruit trees.
So far everything has been successful.
现在时与since 和 for 连用。
I've known him since 1950.
I haven't smoked a cigarette for a year