Tom was about to close the window __________ his attention was caught by a bird.
| A．when |
| B．if |
| C．and |
| D．till |
. Driving a car without insurance can have _____ consequences.
| A．uncertain | B．disastrous | C．potential | D．unworthy |
. Probability is the mathematical study of the _____ of an event's occurrence.
| A．desire | B．likelihood | C．result | D．effect |
. New mineral resources may be discovered during the forthcoming Antarctic _____.
| A．excursion | B．execution | C．extraction | D．expedition |
They have been waiting for many hours to see the singer, but the airplane must have been _____.
| A．behind the times | B．behind schedule |
| C．ahead of time | D．in no time |
Today, housework has been made much easier by electrical _____.
| A．facilities | B．appliances | C．instruments | D．equipment |