单项选择题
Which of the following does an astronomical time clock do？（）
A.Determines the ambient light at night with a photocell.
B.Calculates sunset and sunrise times based on geographical area.
C.Determines the start and end of each of the seasons.
D.Synchronizes the local time displayed with the official world time.
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A.fire proof
B.fiberglass coated
C.plenum rated
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Whichofthefollowingistherecommendedplacementoftherearsurroundspeakersina5.1surroundinstallation？（）
A.Directly to the left and right and slightly in front of the listener
B.Directly to the left and right and slightly behind the listener
C.Above and behind the listener
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Ifthespeakersinaninstallationareoutofphase，thismeansthat（）
A.the subwoofer is at the wrong angle.
B.the front and rear speakers are reversed.
C.the polarity of the speakers are reversed.
D.the angle of the speakers are incorrect.
