as if 是连词，后接从句。网友的两个句子是as if 后省略了成分，我们补全后，看看问题在哪里。

1. The professor paused as if he was expecting his students to ask questions on the point he had just made.

（进行时态的省略，从句省略了 he was）

2. The professor paused as if he was going to expect  his students to ask questions on the point he had just made.

（将来时态的省略，从句省略了 he was going ）

3. The man we followed suddenly stopped and looked as if he was seeing whether he was going in the right direction.

（本句错误在于：see 是瞬间动词，不能延续的动词不能使用进行时态，因为进行时态意味着动作是延续的。上句expect 是延续性动词，就可以用于进行时态。）

4. The man we followed suddenly stopped and looked as if he was going to see whether he was going in the right direction.

（本句正确：see 是瞬间动词，不定式表示将要发生）

【结论】see 是“瞬间动词”，不用于进行时态；expect是“延续性动词”，可以用于进行时态。