The time he has devoted in the past years _______ the homeless is now considered _________ of great value.

All the clerks went home _________ Mr. Yang，for he had to finish his work.

The teacher asked us not to______ our books or dictionaries when we are in the exam.

Haze weather has become common in some major cities in China. We all wonder ________.

s growth is not _____ threat toothers. On _____ contrary, it will bring more opportunities to the world.