有关are/were/did/do疑问句子的用法

1. are 和 were 都是从 be 变来的,be 是一个系词,它的基本意思是“是”.are 是现在时,即表示“现在是”；而 were 是过去时,即表示“过去曾是”.在疑问句中,系词要放在主语之前.例如：Are you a student? 你（现在）是学生吗? Were you a student? 你（过去）曾是学生吗?
2. do 和 did 在“主谓宾”句型的疑问句中作助动词,也要放在主语之前.所谓“主谓宾”句型是指句中有一个“行为动词”.表示人或物的动作行为的词就是“行为动词”.do 用于问现在的行为,did 用于问过去的行为.例如 Do you love her? 你（现在）爱她吗?而 Did you love her? 则是“你曾经爱过她吗?”
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首先，区别它们的性质，arewere是be动词，而did和do是助词。
然后，were和did是are和do的过去时，弄明白了后，我们再看它们所引导的疑问句。
are和were引导的疑问句：Are you a student？Were you a stundent?
did和do引导的疑问句：Do you like apples？Did you like apples...

Are you in Shanghai now ?
Were you in Shangha two weeks ago?
Do you know Shanghai?
did 疑问句很少