The Mekong River, which________ several countries in Southeast Asia, ______to be playing a significant role in the region.

you are reading an article,You’d better _______ the key words and topicsentences.

With so many other people waiting to buy train tickets，we________gave up and chose to take a flight[ ]

That year his total income, with his reward ______, _______ 1500 dollars.[ ]

Could you do me a favor ?——It depends on _____ it is .