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 / couldnt 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 / wasnt 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 / didnt，动词还原，构成否定句。例如：
The famous singer sang some Chinese songs. The famous singer did not / didnt 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 Li look 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