Unluckily, when I dropped in , Dr. Smith ____, so we only had time for a few words.
| A．was just leaving | B．has just left | C．had just left | D．just left |
You'll miss the train ______ you hurry up.
| A．unless | B．as | C．if | D．until |
When you read the book, you' d better make a mark _____ you have any questions.
| A．at which | B．at where | C．the place | D．where |
We'd better hurry ______ it is getting dark.
| A．and | B．but | C．as | D．unless |
I didn' t manage to do it _____ you had explained how.
| A．until | B．unless | C．when | D．before |
_____ he comes, we won't be able to go.
| A．Without | B．Unless | C．Except | D．Even |