单项选择题
Which of the following devices can route electrical signals only when activated by an external control signal？（）
A.Solenoid B.Relay C.Clutch D.Capacitor
单项选择题 WhichofthefollowingistheFIRSTstepatechnicianshouldtakewhentroubleshootingadeviceissue？（）
单项选择题 Howshouldaservicerepresentativeprovideclosureattheendofacallforaclient？（）
单项选择题 Scheduledpreventativemaintenancevisitsshouldbecarriedout：（）
