单项选择题
A.The power supply is faulty and should be replaced.
B.The heat from a heating， ventilation， and air conditioning （HVAC） register is being received as infrared noise.
C.The radio frequency interference （RFI） is being received as noise.
D.A plasma display is emitting infrared noise.
单项选择题 Acustomernotifiestheintegratorthatthesystemkeypadreportstroubleatawindow.Uponinspection，thecustomerfindsthewindowclosedandlocked；thecustomerresetsthesystemanditfailstocorrecttheissue.Whichofthefollowingstepsshouldtheintegratortaketoresolvetheissue？（）
单项选择题 Wheninstallingasecuritysystem，whichofthefollowingconnectorswouldbeusedtoconnectthesecuritysystemtothetelephoneservicedemarcation？（）
单项选择题 Whichofthefollowingdoesanastronomicaltimeclockdo？（）