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And they travel through a universe so large that one star seldom comes near to another. For the most part each star makes its journey in complete loneliness, like a ship on an empty ocean. The ship will be well over a million miles from its nearest neighbor. From this it is easy to understand why a star seldom finds another anywhere neat it.
We believe, however, that some two thousand million years ago, another star wandering (漫游) through space, happened to come near our sun, Just as the sun and the moon raise tides (潮汐) on the earth, so this star must have raised tides on the surface of the sun. But they were very different from the small tides that are raised in our oceans; a large tidal wave must have travelled over the surface of the sun, at last forming a mountain so high that we cannot imagine it. As the cause of the disturbance (动荡) came nearer, so the mountain rose higher and higher. And before the star began to move away again, its tidal pull had become so powerful that this mountain was torn to pieces and threw off small parts of itself into space.
These small pieces have been going round the sun ever since. They are the planets (行星).
第47题：Millions of stars are ________.
[A] following a regular path in space
[B] moving about without a fixed course
[C] seldom wandering about in the universe
[D] always travelling together
更多“DMillions of stars are travelling about in space. A few form. groups which journey togethe”相关的问题
第1题
While paralleling two (2) AC generators using synchronizing lamps only, both lamps will go dark when the generators are _____.
A.running at the same speed
B.grounded
C.of the same polarity
D.in phase
第2题
A.slightly less than the line frequency
B.the same as the line frequency
C.slightly greater than the line frequency
D.All of the above
第3题
A.slightly less than the oncoming generator frequency
B.the same as the bus frequency
C.slightly greater than the bus frequency
D.the same as the bus voltage
第4题
You are attempting to parallel two AC generators, and the synchroscope(同步器) pointer is revolving in the fast direction. This indicates that the frequency of the incoming machine is ______.
A.higher than the bus frequency
B.lower than the bus frequency
C.the same as the bus frequency but out of phase with it
D.the same as the bus frequency and the circuit breaker may be closed at any pointer position
第5题
Which is a function of the voltage regulators used with AC generators？
A.To cut out generators when they are no longer required
B.To cut in additional generators automatically as required
C.To divide the KW load equally between generators operating in parallel
D.To divide reactive current between generators operating in parallel
第6题
A.voltage regulators
B.field rheostats
C.reverse power relays
D.prime mover governors
第7题
The operation of paralleling two alternators requires() to be equal and also in phase
A.the currents
B.the voltages
C.the resistances
第8题
Equal power factors on paralleled AC generators are maintained by an automatic______.
A.voltage regulator
B.reverse power relay
C.reverse current relay
D.governor control switch
第9题
A.an electrical interlock system
B.an automatic paralleling trip switch
C.the synchronizing oscilloscope
D.the reverse current relay
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