我以前从未见过这么高的山。

I had never seen such a tall mountain ___before.

学生们恭敬地站在老师面前。

The students stood respectfully ___before their teacher.

请在会议开始前准备好你的报告。

Please prepare your report ___before the meeting starts.

我宁愿走路也不愿坐公交车。

I'd walk ___before taking the bus.