单项选择题
Copper is often used as an electrical conductor because it （）.
A.has high resistance at low temperatures B.has a highly polished surface C.is able to pass current with little opposition D.holds insulation together well
单项选择题 A device which prints out a permanent record of the plant operating conditions is known as the （）.
单项选择题 Which of the following types of motors is often designed for use in correcting power factor?（）
单项选择题 Power transformers are rated in （）.
