I am very worried because my son ________ most of his spare time ________ playing games on the computer.
| A．concentrates；on | B．concentrates；in |
| C．focuses；to | D．focuses；in |
—May I smoke here?
—If you _______, choose a seat in the smoking section.
| A．should | B．could |
| C．may | D．must |
—Can we ski on this mountain?
—Of course.However, at no time _______ you do so alone.
| A．could | B．might |
| C．need | D．must |
He _______ have completed his work；otherwise, he wouldn’t be enjoying himself by the seaside.
| A．should | B．must |
| C．wouldn’t | D．can’t |
He must have been late for the conference yesterday, _______?
| A．didn’t he | B．hasn’t he |
| C．mustn’t he | D．wasn’t he |
He _______ more visits to his parents.He has been regretting not doing so since they passed away.
| A．should pay |
| B．would pay |
| C．should have paid |
| D．would have paid |