单项选择题
Reheating a hardening component to a temperature lower than the hardening temperature and then cooling it is known as （）
A.low temperature hardening B.case hardening C.annealing D.tempering
单项选择题 Which of the listed effects represents the purpose of heat treating steel?（）
单项选择题 Which of the following nondestructive testing methods can be used to detect a suspected subsurface defect in a tail-shaft liner?（）
单项选择题 To anneal a copper gasket, you should heat the gasket（）
