as if/though+主语+did/had done…好像……（表示现在或将来的情况用过去时；表示过去的情况用过去完成时
例句：
It looks as if it is going to rain.
It looked as if…
Our head teacher treats us as if we were her own children, so all the students in our class think highly of her.
Alan talked about Rome as if he had been there.
