In the chlorination of alkanes, the correct order of reactivity of primary, secondary and tertiary hydrogen atoms is
A. Tertiary-H `gt` Secondary-H `gt` Primary-H
B. Tertiary-H `gt` Primary-H `gt` Secondary-H
C. Primary-H `gt` Secondary-H `gt` Primary-H
D. Secondary-H `gt` Primary-H `gt` Tertairy-H