问题
Several students were working _____the difficult math problem after class. [ ]
A: in
B: to
C: off
D:on
B: to
C: off
D:on
正确答案是：
同类题型
Please call Alan __________ 209 -9696.[ ]
Our school magazine comes out twelve times a year. —- Oh, that’s a _____ magazine.
We have ________ some organizations to help the poor students in the western areas of China.
_________ do you want to join the music club?—Because I want to learn from others about music.
I’m terrified _____ the dark. I go to sleep _____ my bedroom light _____. [ ]