单选

A mean sun is used as the reference for solar time for three reasons. Which reason is NOT acause for use of a mean sun? ______.

  • A.The motion of the apparent sun is along the ecliptic
  • B.Measurement of time is along the celestial equator
  • C.The speed of the Earth’s revolution is not constant
  • D.There are variations in the Earth’s rotational speed
参考答案
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