The correct option is A port / where
An adverb is a word which describes a verb, an adjective or another adverb in a sentence. The relative pronouns where, when, why, whatever etc act as adverbs when they join sentences or clauses. Therefore an adverb which introduces a relative clause is called a relative adverb. 'Where' is used as a relative adverb referring to a particular place that someone or something is in or that they go to. Thus, option A is the correct answer.