_______some people some here for a short break , others have decided to stay forever.
| A．Because | B．If | C．Once | D．While |
Every few years, the coal workerstheir lungs X-rayed to ensure their health.
| A．are having | B．have | C．have had | D．had had |
The plan _________ just because people were unwilling to cooperate (合作).
| A．broke down | B．pulled down | C．turned down | D．put down |
Jack, I’m afraid I’ll turn to you．I think chemistry is _______ physics．
| A．as a difficult subject as | B．a subject the same difficult as |
| C．as difficult a subject as | D．the same difficult subject as |
Not until then did I find it _____ to do the job that way.
| A．is easier | B．easier | C．was more easily | D．more easily |
Most of the professors _____ to our school were from South Africa．
| A．invited | B．to be invited | C．being invited | D．had been invited |