that引导的是什么从句,先行词是什么

　　I'd like to come on to that question later.

　　我想以后再讨论那个问题。

　　That is no way to treat another human being.

　　那绝不是对待他人的方式。

　　Had I known that I would never have come.

　　要是早知道，我绝不会来的。

　　Keep going like that ─ you're doing fine.

　　就这样做下去——你做得蛮不错嘛。

　　We had to work within the parameters that had already been established.

　　我们必须在已设定的范围内工作。