[单选题]
By what primary heat transfer mechanism does one end of anynq o77zo1 kny8:s)ek iron bar become houz 6cerlqx8u(d8 ub.; t when the other end is pladr6 u 8(ce ubl;qxu8z.ced in a flame?
A. natural convection
B. conduction
C. radiation
D. forced convection
