一变：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.→Icould 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 wasnot/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didnot/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.