Synonyms are words that mean the same but are worded different. For example knife and blade. They both mean a sharp pointed weapon but sound different. So in this case the answer is going to be option D "Secret; furtive." A secret is something kept between two or more people that they dont want other people to know, furtive is trying to avoid somone because of guilt or because you dont want that person to know. (another word for secret)
Hope this helps!