In which sentence is the capitalized word used correctly?

a) the principle welcomed the students back from vacation.
b) we visited the capitol building during our visit to washington.
c) the students were instructed to use capitol letters on the form.
d) my friend said that we should not participate, as it is a matter of principal.

i'm thinking the answer is d, but i am not 100% about it.

explain your answer clearly and thoroughly so i can understand. : )

you! ^-^

The answer would be B) since "Capitol" means a building in which state legislative body meets and the word "Capitol" used in C) is wrong since the correct spelling (capital) refers to letters and words. D) would also be wrong since the Principal means the most senior or most important person in a group (like a school principal). Principle means a "fundamental basis of a system of thought and belief" An example of Principle would be "The basic principle was that those who worked hard would be rewarded".

I hope my response did help and if you need clarification do reply and I will try my best to clarify it (: