[单选题]
By what primary heat trans 5*p6 pehyr*7lv-mdd jfer mechanism does one end of an iron bar become h3z 1ssgiv e*vurd)2 r+ot when the other end is placed in)u2desv3 r*v+ is1zrg a flame?
A. natural convection
B. conduction
C. radiation
D. forced convection
