几个英语句子帮忙解释语法

几个英语句子帮忙解释语法
最近在读一些名著名篇,有几句话不懂它的语法结构,
1.the unpunctual man is always complaining that he finds no time to answer letters.为什么是always complaining而不是三单?2.unpunctuality is very harmful when it comes to doing one's duty.句中comes to doing,to 后面不应该加原形么,这种句子碰到好几次,不明白to怎么能跟doing