[单选题]
By what primary heat tran+ ccz t ow)p0 6;xlmjv3wne12ssft 4* ferp*3lig wom, +7nxde6aer mechanism does one end of an iron bar become hot when the other end is plamd+*4f,eeg 3po6wn it*ax rl7ced in a flame?
A. natural convection
B. conduction
C. radiation
D. forced convection
