现在进行时：
I'm doing my homework.
You are swimming.
She is chatting with a boy.
The bird is singing.
I am reading.
过去进行时(往往会出现时间状语,最后两句我加了）：
I was doing my homework.
You were swimming.
She was chatting with a boy.
The bird was singing last night.
I was reading just now.