Scientists are convinced the positive effect of laughter_____physical and mental health.
| A．of, at | B．by, in | C．of, on | D．on, at |
At the Copenhagen conference, all the countries were called on to do all they could to control greenhouse gas emissions________it was too late.
| A．when | B．after | C．until | D．before |
Mr. Smith’s decision to attend_________ceremony tomorrow can be seen as________gesture of his intention to improve ________the relationship.
| A．the, a, the | B．a, a, the | C．the, the, a | D．a, the, a |
You can’t complain of being lonely_______you don’t make any effort to communicate
with others.
| A．when | B．until | C．unless | D．once |
How long do you think _______ the computer company turns out a new product?
| A．it will be that | B．will it be until | C．will it be since | D．it will be before |
— Why do you look so angry?
— He insists on my presence here, but I can see it makes no difference ______.
| A．I am here | B．I was here | C．me to be here | D．my being here |