it's a waste of time 后面跟to do 还是doing ?

doing sth
例如： It is a waste of time working on this problem.
类似的句型有It's no use /no good/ a waste of time doing sth

it's a waste of time to do
浪费时间做某事,固定用法

应该是doing sth

这是一个倒装句

it`s 是形式主语

主语其实是doing sth.

to do

是doing sth正确说法

to do