For eutectoid steel, the ideal quenching medium should have a cooling characteristic of ( ).
A.
Cooling speed is as slow as possible.
B.
The cooling rate is as fast as possible at 550 ℃and slow at 250℃.
C.
Cooling speed is as fast as possible.
D.
The cooling rate is as slow as possible at 550 ℃and fast at 250℃.