1.wasn't是be动词isn't的过去时,用于过去进行时.
如：1.he wasn't at home yesterday.
2.I wasn't doing my homework yesterday,I was reading books.
2.didn't是“do" "does"的过去时,用于过去现在时.
如：1.I didn't go to the library last week.
2.he didn't take a shower until his mother came back.
3.isn't是一般现在式,后面一般加动词--ing形式
如：1.he is dancing in the gym
2.is she playing football on the playground?