What was the “white man’s burden” that Kipling speaks of in his poem of the same title ?

What was the “white man’s burden” that Kipling speaks of in his poem of the same title ?

A. The pressure of conforming to preexisting social conventions
B. The burden of white colonizers who are forced to learn to live in new lands
C. The Eurocentric idea that the colonizer has a social responsibility to civilize other nations
D. The concept that all white men do not the same imperial duties