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肯定句变为否定句

【技巧1】当句中含有情态动词或助动词could，would，should等时，可直接在其后面加not构成否定句。例如：

I could get you a concert ticket. → I could not / couldn't get you a concert ticket.

【技巧2】当句中含有系动词was，were 时，可直接在其后加not构成否定句。例如：

I was on the Internet when you called me. → I was not / wasn't on the Internet when you called me.

【技巧3】当句中谓语是除情态动词、助动词、系动词was,were以外的动词时，在该动词之前加did not / didn't，动词还原，构成否定句。例如：

The famous singer sang some Chinese songs. → The famous singer did not / didn't sing any Chinese songs.