by的理解（conclude by doing sth）

He concluded by wishing everyone a safe trip home.

这里的by必须要翻译出来吗？还有是否被动语态， 他通过祝愿所有人一路平安结束？ 如何感觉翻译别扭。

by 表示方法，conclude by doing sth 的意思是“通过做某事来结束（讲话或发言）”。你的句子意思：

He concluded by wishing everyone a safe trip home.

他通过祝愿大伙回家一路平安来结束讲话。

变通一下就是：他讲话结束时祝愿大伙回家一路平安。

再如：

She concluded by saying she was proud to be from Salford. 她结束时说，身为索尔福德人她感到非常自豪。

May I conclude by thanking our guest speaker. 最后我要感谢大家的演讲嘉宾。

He concluded by pointing out the danger of disregarding his advice. 他结束时指出无视他忠告的危险性。

I’d like to conclude by thanking everyone who has worked so hard to make this conference possible . 最后我想感谢诸位，正是因为诸位的努力会议才得以进行。