On the basis of accompanying isothermal transformation diagram for a 0.45 wt% C iron-carbon alloy, which heat treatment could be used to isothermally convert a microstructure that consists of proeutectoid ferrite and fine pearlite into one that is composed of proeutectoid ferrite and martensite?

(A) Austenitize the specimen at approximately 700°C, rapidly cool to about 675°C, hold at this temperature for 1 to 2 s, and then rapidly quench to room temperature
(B) Rapidly heat the specimen to about 675°C, hold at this temperature for 1 to 2 s, then rapidly quench to room temperature
(C) Austenitize the specimen at approximately 775°C, rapidly cool to about 500°C, hold at this temperature for 1 to 2 s, and then rapidly quench to room temperature
(D) Austenitize the specimen at approximately 775°C, rapidly cool to about 675°C, hold at this temperature for 1 to 2 s, and then rapidly quench to room temperature.

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