单项选择题
When would you ground an electric hand tool?（）
A.When it is a DC machine B.When it is an AC machine C.Any machine that operates on over 100 volts D.Only when working on wet steel plates
单项选择题 The load between two steam-driven alternators operating in parallel may be adjusted by varying （）
单项选择题 The purpose of the commutator and brushes on a DC generator is to（）
单项选择题 DC generators are classified according to the manner in which（）
