In which sentence is the italicized word used correctly?

AThe principle welcomed the students back from vacation.
BWe visited the Capitol building during our visit to Washington.
CThe students were instructed to use capitol letters on the form.
DMy friend said that we should not participate, as it is a matter of principal.

Verified Answer :

Hagrid

The right answer for the question that is being asked and shown above is that: "D) My friend said that we should not participate, as it is a matter of principal." the sentence that is the italicized word used correctly is this D) My friend said that we should not participate, as it is a matter of principal.

The answer is B I know because I picked D and it was wrong