陈述句改疑问句,如果有be动词或情态动词的话就可以提前.例如：He is a student.Is he a student?
You must study hard to get good grades.
Must I study hard to get goodd grades.
如果没有be动词,就要加助动词.加助动词可以是do/does/did,do是原形,does是三单,did是过去式.当用到does的时候,原来的动词要变为原形.
例如：I/They study hard.Do you study hard?
She studies hard.Does she study hard?（加了does以后,studies还原为study.）
She/I/He studied hard.Did she/he/you study hard?
还有在改成疑问句后,人称就要改变.she/he/they不用改变,但是we/I要改成you等等.