—What caused the party to be put off?
—__________ the invitations.
| A．Tom delayed sending | B．Tom’s delaying sending |
| C．Tom delaying to send | D．Tom delayed to send |
After several years of observation, the research group ______ the conclusion that language acquisition is faster when students ______ to the situation where it is spoken.
| A．has come to; expose | B．have arrived at; are exposed |
| C．has concluded; are exposed | D．have reached; expose |
It will be many years ______the doctors and medical scientists can find _____ for cancer.
| A．since; cures | B．when; treatments | C．before; cures | D．until; treatments |
We have to ______ everything question in detail ______ we take action.
It is clear that no use can be made ______radium _____we don’t know clearly the characteristics of it.
| A．from; if | B．of; unless | C．from; unless | D．of; if |
From my point of view, the theory that ______ by the scientist is not quite scientific.
| A．was risen | B．brought up | C．had been raised | D．was put forward |