单项选择题

After Venus passes the point of greatest elongation east in its orbit，the first position in which the elongation will be zero is（）.

A.superior conjunction
B.inferior conjunction
C.opposition
D.None of the above; the elongation will never be zero

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单项选择题
A variable star is one that（）.

A.exhibits a change in magnitude
B.has a changing declination
C.is increasing in SHA
D.is also known as a red giant
单项选择题
A star that suddenly becomes several magnitudes brighter and then gradually fades is a（）.

A.double star
B.variable star
C.nova
D.nebula
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