Doctors have said that as many as 50% of thepatients don’t take medicine as

The two girls are so alike that strangers find_______difficult to tell one from the other. [ ]

There is a chess match between a Korean player and AlphaGo(阿尔法).—It’s very amazing. Playing _____ chess is usually ________ one-to-one game.

Having proper motivation is not _______ —it is another key to success.

If he had spent more time practicing speaking English before, he _____ able to speak it much better now.