Radicals on carbon atom are stabilised when they are in more substituted position that means tertiary radical is more stable than secondary and secondary is more stable than primary radical. Therefore, [B] is least stable followed by [C][A] and [D] are most stable ones. Out of [A] and [D],[A] is more stable as it has more α-hydrogen atom than [D], which Lead to more number of hyperconjugated structures. Correct order of stability is [B]<[C]<[D]<[A]