Which of the following best captures Kant's Formula of Humanity as End?

a) "I ought never to act in such a way that I could not also will that my maxim should become a universal law."

b) "Act in such a way that you treat humanity, whether in your own person or in any other person, only as an end, never as a means."

c) "Never make an exception for yourself."

d) "Act only on that maxim by which you can at the same time will that it should become a universal law."

e) "Act in such a way that you treat humanity, whether in your own person or in any other person, always at the same time as an end, never merely as means."