一般疑问句：
如果是带be动词的句子,把be动词提前就可以了,如：
He is doing his homework.
Is he doing his homework?
They were at home yesterday.
Were they at home yesterday.
如果是实义动词的,则要在句首加一个相应时态的助动词,因为前面已经有助动词了,实义动词就要用原形,如：
He goes to school by bike every day.
Does he go to school by bike every day?
They went to Beijing last week.
Did they go to Beijing last week?
否定句：
如果是带be动词的,在be动词后面加not就可以了,be动词可以和not连在一起缩写,如：
She is a student.
She isn't a student.
We were at school yesterday.
We weren't at school yesterday.
如果是实义动词的句子,在主语后面用相应时态的助动词加not,可以缩写,后面的实义动词变回原形,如：
She goes to work by bus every day.
She doesn't go to work by bus every day.
They bought a TV yesterday.
They didn't buy a TV yesterday.
