1. It’s not ________ good idea to surf the Internet for hours on ________ end without a rest.
A. the; an B. a; an C. a; / D. the; /
2. With everyone’s face ________ behind masks, it’s hard to tell who they really are.
A. hidden B. hiding C. having hidden D. to hide
3. Many foreign students choose Chinese as a second language, ________ they think will be good for their future career.
A. what B. that C. which D. where
