单项选择题
A.2.5 times as bright as a second magnitude star B.3 times as bright as a second magnitude star C.5 times as bright as a second magnitude star D.10 times as bright as a second magnitude star
A.has a declination equal to twice that of the Sun B.comprises two stars that appear close together C.is twice as bright as a single star D.suddenly becomes much brighter and then fades
A.the Sun B.the Moon C.Venus D.None of the above