It became obvious that all her complaints were in vain.

很明显她所有的抱怨都是白费口舌

He stopped at the door, waiting in vain for her to acknowledge his presence.

他停在门口，徒然地等着她跟自己打招呼。

My efforts were not in vain.

我的气力没有白费。

Our efforts were not in vain.; we didn't waste our energy.

我们的力气没有白费。

In vain he declared his innocence; he was dismissed with no better answer.

他宣称自己无罪，却徒劳无功；他没有更好的回答就被解雇了。

Evidently she was racking her head in vain--it seemed manifest that she must give the matter up.

显然，她徒劳地绞尽脑汁——显然她必须放弃这件事。