第1个回答 2007-08-11
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?本回答被提问者和网友采纳
第2个回答 2007-08-11
先说wasn't和isn't
着两个都是be 动词.只是时态不一样.
前者用语一般过去,后者用于现在时态.
都表否定.
通常根据句子意思来确定时态.
例如:I wasn't in the hospital yesterday. 我昨天没有在医院(过去)
She isn't a good girl. 她不是一个好女孩(目前的情形)
再说didn't
是“do" "does"的过去式,是助动词。
用法和do,does一样
只是要根据时态人称来变化。
例如：He didn't buy that expensive book.他没有买那本昂贵的书
上一楼举的例子也不错，你可以参考一下
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