In Hofmann degradation of amide Me the important step is the migration of

Question

$\begin{array}{1 1}(a)\;\text{an alkyl group without its }e^{\ominus}\text{ deficient N atom}\\(b)\;\text{an alkyl group with its electron pair to }e^{\ominus}\text{ deficient N-atom}\\(c)\;\text{an alkyl group with its electron pair to }e^{\ominus}\text{ deficient O-atom}\\(d)\;\text{an alkyl group with its electron pair to }e^{\ominus}\text{ rich N atom}\end{array}$