1、肯定式结构:主语+be+动词-ing形式+其他.
例如:We are running now.
2、否定式结构:主语+be+not+动词-ing形式+其他.
例如:They aren’t doing their homework.
3、一般疑问句式结构:Be+主语+动词-ing形式+其他?
例如:Is she having English lesson?回答:肯定Yes, she is. 否定:No, she isn’t.
4、特殊疑问句式结构:疑问词+be+主语+其他?
例如:What is he doing now?回答:He is swimming.
