1.I'm afraid I can't. 恐怕我不能来。

　　2. I have things to do. 我有事情要做。

　　3. I'm kind of busy. Maybe later. 我有点儿忙,也许以后吧。

　　4. I'm busy right now. Sorry. 我现在很忙，抱歉。

　　5.I can't come over right now. 我不能马上过来。

　　6.take a rain check on sth (改期)