介词短语 but for

Bat for + 原因，解释某事没有发生的原因，主句用虚拟语气 would have/has。类似于中文的“要不是因为 A，可能就会发生 B”。

But for the traffic, I would have been here an hour ago.
要不是因为交通（拥堵），我可能一小时前就到了。

They would have been badly injured but for the fact that they were wearing seat belts.
要不是他们扎了安全带，他们可能严重受伤了。