A successful scientist needs _____ if he wants to make hypothesis (假设) of how processes work and how events take place.
| A．permission | B．penetration | C．imagination | D．convention |
We apologize for any inconvenience you _______ have been caused by the delay of the flight.
| A．may | B．would | C．must | D．need |
The police say there is a $50,000 _______ for any information that helps them find the killer.
| A．income | B．fee | C．bill | D．reward |
Most whales must come up for air after several minutes, _______ a few can stay under water for an hour or more.
| A．while | B．or | C．for | D．so |
The numbers that researchers get from the experiments can be _______, just like number puzzles.
| A．disappointing | B．inspiring | C．worrying | D．confusing |
_______ the house is empty, memories flood my mind of a time when it was filled with life.
| A．Since | B．Unless | C．As if | D．Even though |