于事无补----be of little avail

例句：
A: He's always complaining about air pollutioii.
他总是抱怨空气污染。
B: Complatning is of little avalL He'd better take actions to eliminate it.
抱怨于事无补，他最好采取行动来消除空气污染。

同义词：
be of no avail