[单选题]
By what primary heat transfer mechani2gedjr;e501g2/gp5tqyh ) j5n jjye a sm does one end ;m/ xr8y6 tbxlof an iron bar become hot when the r 86;ytlx xm/bother end is placed in a flame?
A. natural convection
B. conduction
C. radiation
D. forced convection
