_________ caused the accident is still a complete mystery.
| A．What | B．That |
| C．How | D．Where |
The audience ______ when they heard the humorous story.
| A．burst into laughing | B．burst out laughter |
| C．burst into laughter | D．burst in laughing |
— What about ______ lecture you attended yesterday?
— To tell the truth, it was too boring．I can’t stand ______ lecture like that．
| A．a; the | B．the; a | C．the; 不填 | D．the; the |
From time to time a crocodile has snatched someone _______ he or she is even aware that the crocodile is there.
| A．when | B．until | C．since | D．before |
_____ unemployment and crime are high, it can be assumed that the latter is due to the former.
| A．Before | B．Where | C．Unless | D．Until |
—I’m sorry．That wasn’t of much help．
— Oh, _______ . As a matter of fact，it was most helpful．
| A．sure it was | B．it doesn’t matter | C．of course not | D．thanks anyway |