Which of the following is NOT a formulation of the categorical imperative?

Question $10$ Select one:

a$.$

Always treat humanity, whether in yourself or in others, never merely as a means but always as an end in itself.

b$.$

Act only according to that maxim by which you can at the same time will that it should become a universal law.

c$.$

Act as if the maxims of your action were to become by your will a universal law of nature.

d$.$

Always treat humanity, whether in yourself or in others, never as a means to an end.