单项选择题
It is well known that the whole power distribution of the ship’s electrical services mainly depend on the（）.
A.sub-boards B.main switchboards C.emergency switchboards D.distribution boards
单项选择题 How do you treat someone suffering from electrical shock after you secure the source?（）
单项选择题 Tools with （）handles should be used to check electric circuit.
单项选择题 Before doing maintenance on electrical equipment, you should （）.
