_____ puzzles me most is that I don’t know ______ the difference between the two lies.
| A．What, how | B．What, where | C．That, what | D．How, which |
—Are you coming to Alice’s party?
—I’m not sure.I _______ go to the concert instead.
| A．must | B．would |
| C．should | D．might |
—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 |