must/ must't / have to/ don't have to

must 必须做某事

must't  绝对不能做某事

have to 不得不做某事，必须做某事

don't have to 不是必须做某事，可做可不做，可以选择

I must study English so ...

must .... because...

have to ...so ...

have to ...because...

must't ....so..

must't ....because...

don't have to...so...

don't have to ...because...