单项选择题
A switchboard for an AC electrical system requires the use of which of the following devices（）.
A.Frequency meter B.Ohmmeter C.Induction voltage regulator D.Current transformer governor
单项选择题 The part of the shipboard electrical system used to control the distribution of power to the branch circuits, is the （）.
单项选择题 A semiconductor is a material with a （）.
单项选择题 The sub-multiple prefix “micro” means （）.
