The students didn’t manage to work out the problem ________ their teacher had explained how．

A．when

B．until

C．unless

D．as

________ I can see, the weather is not likely to change in a few days．

A．As well as

B．As far as

C．As long as

D．As soon as

Einstein was given the Nobel Prize ________ Physics in 1921．

A．in

B．at

C．on

D．for

________ I came into the office, the teachers were having a meeting．

A．While

B．When

C．Once

D．Since

－Can I pay the bill by check?

－Sorry, sir．But it is the management rule of our hotel that payment ________ be made in cash．

A．shall

B．need

C．will

D．can

I ________ you, but I didn’t think you would listen to me．

A．could have told

B．must have told

C．should tell

D．might tell

－Would you mind giving your advice on how to improve our business management?

－If you make ________ most of the equipment, there will be ________ rise in production．

A．/;/

B．the; a

C．/; a

D．the;/

________ the earth to be flat, many feared that Columbus would fall of the edge of the earth．

A．Having believed

B．Believing

C．Believed

D．Being believed

After the Arab states won independence, great emphasis was laid on expanding education, with girls as well as boys ________ to go to school．

A．to be encouraged

B．been encouraged

C．being encouraged

D．be encouraged

________ their homework, the children went for a walk．

A．When they were doing

B．After they have done

C．Having done

D．They had done