[单选题]
By what primary heat to*7 k3tznof86l; mvboysz+ p)b ) (2kbzup 06kma8lqf)d7vyg ransfer mechanism does one end of an iron bar become hot when the other end is placed in a flame?va2l6zb0gpk)q 8kbdumy )7 f(
A. natural convection
B. conduction
C. radiation
D. forced convection
