She is . . . . . . . . only person here that speaks Japanese.

The correct answer is D. no article.

The word "only" indicates that the person being referred to is unique or one of a kind. In this case, the person is the only person in the group who speaks Japanese. Therefore, we do not need to use an article before the noun "person."

If we used an article, it would imply that there are other people in the group who speak Japanese. For example, if we said "She is the only person here that speaks Japanese," it would mean that there are other people in the group who speak Japanese, but she is the only one who speaks it fluently.

However, in this case, we are simply stating that the person is the only person in the group who speaks Japanese. We are not making any comparisons to other people in the group. Therefore, we do not need to use an article.