Determine whether the given set S is a subspace of the vector space V. A. V=Mn(R), and S is the subset of all upper triangular matrices. B. V=C2(I), and S is the subset of V consisting of those functions satisfying the differential equation y′′=0. C. V=R2, and S is the set of all vectors (x1,x2) in V satisfying 5x1+6x2=0. D. V=P5, and S is the subset of P5 consisting of those polynomials satisfying p(1)>p(0). E. V is the vector space of all real-valued functions defined on the interval [a, b], and S is the subset of V consisting of those functions satisfying f(a)=5. F. V is the vector space of all real-valued functions defined on the interval [a, b], and S is the subset of V consisting of those functions satisfying f(a)=f(b). G. V=Mn(R), and S is the subset of all n×n matrices with det(A)=0.