—I wonder why Susan looks worried today.
—I’m not sure, but she _____a small accident driving here.
| A．could have | B．might have | C．might have had | D．must have had |
Father made a promise ______ I passed the exam, he would buy me a PS4.
| A．if | B．that if | C．whether | D．that |
--- Alex came back home the day before yesterday.
--- Really? Where ______ at all?
| A．had he been | B．has he been | C．had he gone | D．has he gone |
The dangerous virus ______ in the next few weeks in the laboratory can cause fatal diseases.
| A．studying | B．studied |
| C．to study | D．to be studied |
How can you expect him to make any progress ______ you never give him a chance to have a try?
| A．when | B．unless | C．once | D．until |
Getting all your teammates ______ in a game is the key to victory.
| A．trapped | B．settled | C．stuck | D．involved |