Answer: The right answer is the B) Somos seis personas.
Explanation: Just to elaborate a little on the answer, it can be added that the question that Eva has asked Laura is "How many people live in your house?" The answer, therefore, should include a number. Option A means "Yes, we have never lived together," so it can be discarded. Option C means "No, we are not many," so it can be discarded too. Finally, option D means "Yes, all (of them) live with me." The right answer is option B, since it translates as "We are six people."