单项选择题
A.secure the electric supply
B.ventilate area to remove smoke
C.start the fire pump and lead out hose
D.apply foam
单项选择题 When working on a high voltage circuit, you should always have another person present with you.This person should have a good working knowledge of （）
单项选择题 An emergency generator, driven by an internal combustion engine, shall be tested under load for a minimum of 2 hours at least once every （）
单项选择题 Before any work on electrical or electronic equipment is performed, which of the following precautions should be carried out （）