Use the First Step of the Reaction of 2-Bromo-2-Methylpropane with Water

Use the first step of the reaction of 2-bromo-2-methylpropane with water, shown below, to answer the following question(s) .
-In the following generic reaction between a halogen (X) and an alkane (R) , which of the following steps occurs slowly due to low concentration of reactants?

A) X⎯X → 2X∙
B) X∙ + R → HX + R∙
C) R∙ + X⎯X → RX + X∙
D) X∙ + R∙ → RX
E) X∙ + X∙ → X⎯X
F) R∙ + R∙ → R⎯R