Age hardening is a process done at______________?

A. Heating up to 200 – 450°C for 15 – 30 min and quenching in water
B. Heating at 700°C for 10 – 15 min and quenching in water
C. Heating at 700°C for 1 hour and quenching in water
D. Heating above 700°C for 30 min and quenching in water