肯定句:主语+
be动词(am /is /are)+动词ing+其他。
Look! They are playing football.
否定句:主语+be动词(am /is /are)+not+动词ing+其他。
Tom isn't watching TV now.
一般疑问句:Be动词+主语+动词ing+其他。
回答:Yes,主语+be. 或 No,主语+be not.
Are you reading at the moment?
Yes, I am./ No, I am not.
特殊疑问句:特殊疑问词+一般疑问句
Who are you waiting for?
I am waiting for my mother.