—You seem to get lost. Need help?

—       

A．Yes, could you please help me with the bag?

B．Yes, give me a hand, please

C．I am looking for the way to the station.

D．Help me find my key, please.

在过冷奥氏体转变图中，与珠光体转变开始线相切的那个冷却速度叫做（）速度。

A.最高冷却

B.最低冷却

C.理想冷却

D.临界冷却