Homophones are words that have the same or similar pronunciations, but different meanings. 'Principle' and 'principal' are homophones.
'Principle' is an accepted or professed rule of action.
'Principal' is more relevant to the given sentence, as it completes it in meaning: a person going for a meeting.
Hence option B is correct and A is incorrect.
Options C and D are incorrect for the same: C cannot be correct because A is incorrect, and D cannot be correct because B is correct.