ought to

We ought to leave for the airport now if we want to catch the last flight at midnight.

(Chinese) 如果我们想赶上子夜的末班飞机，现在就应当出发去机场。

You ought to apologize to your sister for your rude comments during dinner last night.

(Chinese) 你应当为你昨晚晚餐时的粗鲁言论向你姐姐道歉。