问题

Listen! I hear some birds ___________ thetree.

A:singin
B:while
C:until
D:singing on

正确答案是：

同类题型

（题文）In the last few years, China ___ great achievements in environmental protection.

I look at the menu before I make an order— Of course. ___________, madam.

Shall we __ for twenty minutes and have a cup of coffee?[ ]

I think _________ necessary for students totake an interest in all subjects.

He worked , but he felt .