Which reaction occurs via a free-radical mechanism?

A.     ${{\text{C}}_2}{{\text{H}}_6} + {\text{B}}{{\text{r}}_2} \to {{\text{C}}_2}{{\text{H}}_5}{\text{Br}} + {\text{HBr}}$

B.     ${{\text{C}}_2}{{\text{H}}_4} + {\text{B}}{{\text{r}}_2} \to {{\text{C}}_2}{{\text{H}}_4}{\text{B}}{{\text{r}}_2}$

C.     ${{\text{C}}_4}{{\text{H}}_9}{\text{I}} + {\text{O}}{{\text{H}}^ - } \to {{\text{C}}_4}{{\text{H}}_9}{\text{OH}} + {{\text{I}}^ - }$

D.     ${{\text{(C}}{{\text{H}}_3})_3}{\text{CI}} + {{\text{H}}_2}{\text{O}} \to {{\text{(C}}{{\text{H}}_3}{\text{)}}_3}{\text{COH}} + {\text{HI}}$

A