The correct answer for this would be option B. Based on the given sentence above, the highlighted part of the sentence which is "<span>who had been to the mansion before," is called an appositive phrase. This is considered as an appositive phrase because it renames or describes the noun next to it. Hope this helps.</span>
You might want to add more descriptions of the subject you are researching, or use quotes from articles to help it be known that it is genuine research. Make sure to cite the article and use in-text citation to avoid plagiarism.