Which of the following is a true​ statement? A. The proof is complete since W is a subspace of . The given set W must be a vector space because a subspace itself is a vector space. B. The proof is complete since W is a subspace of . The given set W must be a vector space because a subspace itself is a vector space. C. The proof is complete since W is a subspace of . The given set W must be a vector space because a subspace itself is a vector space. D. The proof is complete since W is a subspace of . The given set W must be a vector space because a subspace itself is a vector space.