The correct answer is complete subject. Assuming that the words in bold are <em>Melinda and Belinda, her twin sister, </em>then the answer is complete subject. A complete subject includes not only the actual subject of a sentence, but also all words directly connected to it (such as <em>her twin sister). </em>If only Melinda and Belinda were bolded, then it would be a compound subject (consists of more than one subject).