单项选择题

When is the guided tour of the campus given

A．Only during the first week of classes.
B．Whenever students ask for them.
C．Only in the afternoon.
D．In the afternoon.

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问答题

[听力原文]Light travels at a speed which is about a million times faster than the speed of sound. In one second, light travels about 300,000 km, but sound travels only 0. 334 kin. You can get some idea of this difference by watching the start of a race. If you stand some distance away from the starter, you can see smoke come from the referee’s gun before the sound reaches your ears.This great speed of light produces some strange facts. Sunlight takes about 8 minutes to reach us. If you look at the light of the moon tonight, remember that the light rays left the moon 1.3 seconds before they reach you. The nearest star is so far away that the light which you can see from it tonight started to travel towards you four years ago. The light from some of tonight’s stars may have started on its journey to you before you were born.

单项选择题

In approximately what year was the first maser built

A．1917.
B．1951.
C．1953.
D．1957.

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