What is the difference between Kant's categorical imperative and a prima facie duty?

Select one:

a$.$ A categorical imperative is an absolute ethical demand, whereas a prima facie duty may be overridden by the demands of other duties.

b$.$ The different formulations of Kant's categorical imperative describe different types of prima facie duties.

c$.$ Prima facie duties promote prosocial behaviour, whereas Kant's categorical imperative entails an absolute ethical principle.

d$.$ A prima facie duty is an absolute ethical demand, whereas the categorical imperative may be overridden by the demands of other duties.