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/whattime，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