一般现在时和一般过去时句型结构的异与同：
(1) 一般现在时表示某人某物现在的状态，性质等．eg:
I am a teacher now.
She(He) is a singer.
We / They / You are happy.
(2) 一般过去时表示过去时间内某人某物存在的状态，性质等．eg:
I was a teacher last year.
She / He was a singer.
We / You / They were happy.
例句：
It was a duckling. Now it is a duck.
It was rainy yesterday. It is windy today.
The sofa was under the shelf. Now it is under the window.
练一练：
We___ (be) at home last night.
A. are
B. is
C.was
D. were
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