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.

→ 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.
二变：陈述句变为一般疑问句
【技巧1】移动词语的位置。将was，were, could，would，should等移到句首。例如：
He could pack his things himself.

→ Could he pack his things himself?
【技巧2】添加助动词did。谓语是除情态动词、助动词、

系动词was, were以外的动词时，在主语之前加did，动词还原。

例如：
Mr Li looked very old.

→ Did Mr Lilook very old?
三变：陈述句变为特殊疑问句
【技巧1】确定疑问词：人who / whom，物what，地点where，时间when / what time，原因why，频率how often，长度how long，距离how far等等。例如：
They gave the concert last night.

→ When did they give the concert?
【技巧2】辨认结构形式：

疑问词+情态动词/助动词/ was / were / did +主语+...?

例如：
The accident happened near the station.

→ Where did the accident happen?