In practical production, when metals are cooling, .在实际生产中,当金属冷却时,下列说法正确的是()
A.actual crystallizing temperature(实际结晶温度) is always below theoretic crystallizing temperature(理论结晶温度) B.actual crystallizing temperature is always equal to theoretic crystallizing temperature C.actual crystallizing temperature is always higher than theoretic crystallizing temperature D.actual crystallizing temperature and theoretic crystallizing temperature have no relationship