Kant's Categorical Imperative Contains Three Parts

Kant's categorical imperative contains three parts. Maxim 3 states, "Act only so that the will through its maxims could regard itself at the same time as universally lawgiving". What does this mean?

A) Humans deserve respect as autonomous, rational actors and human dignity should never be ignored.
B) It is a test to check whether other rational actors would endorse our judgement of a certain situation.
C) It is a consistency test to check whether the principle underlying an action could be followed by everyone.
D) The maxim celebrates the inherent subjectivity of our moral decisions.