Reheating a hardening component to a temperature lower than the hardening temperature and then cooling it is known as （）

A.Develop ductility
B.Improve machining qualities
C.Relieves stresses
D.All of the above

A.Dye penetrant
B.Magnetic particle
C.Ultrasonic
D.All of the above

A.and quench it in oil
B.cherry red and quench in water
C.and let it cool slowly in the air
D.and carbonize