English is _________ useful language in the world.

Your schoolbag isvery nice.– __________.

How do you like this piece of music by Tan Dun — Well, of all the music that he has written, I think this is his ________ one.

How lucky! The tourist stopped at the last moment..—Indeed! One more step and he ________ off the cliff（悬崖）

Whose Chinese book is this—It could _____. He studies Chinese.