The bridge is so important to the people here that once ________ it must be carried out without delay.

Birds'singing is sometimes a warning to other birds________away.

You can see the bright Yaoming today, but can’t imagine what a hard time he had   himself home and abroad before.

Knowing office rules—whether _____ or not—is critical, especially for young job seekers.

Once______ in the exam, the students who’ve done it would be punished.