---Don't put the waste on the ground.
---Oh, I'm very sorry. I ________ the dustbin（垃圾箱） there.
| A．don't see | B．isn't seeing | C．didn't see | D．haven't seen |
--- Who ______ it be that is singing in the next room?
--- It _______ be Lucy, but I am not sure.
| A．can ; may | B．may ; can | C．can; must | D．must; may |
Not until World War II ______ to use new chemical techniques to purify penicillin.
| A．they managed | B．that they managed |
| C．did they manage | D．they didn’t manage |
--- What did the manager say at yesterday’s meeting?
--- So you______ to him carefully.
| A．won’t listen | B．weren’t listening |
| C．hadn’t listened | D．haven’t listened |
--- Did Jack come back early last night?
--- Yes. It was not yet eight o’clock ______ he arrived home.
| A．before | B．until | C．when | D．af ter |
In some countries citizens are ______ to vote, and if they don’t they get fined.
| A．demanded | B．suggested | C．prevented | D．required |