下列公式中一定成立的是______。A．πA1,A2(σF (E))≡σF (πA1,A2 (E))B．σF (E1×E2)≡σF (E1)×σF (E2)C．σF (E1-E2)≡σF (E1)-σF (E2)D．πA1,A2,B1,B2 (EE)≡πA1,A2 (E)πB1,B2 (E)
A．(A, B, D, C, F, E, I, J, H, G)B．(A, B, D, C, E, F, I, H, G, J)C．(B, F, G, E, A, I, D, C, H, J)D．(B, F, G, J, A, E, D, I, C, H)
A．(C, B, D, A, F, E, I, J, G, H)B．(C, B, D, A, E, F, I, G, J, H)C．(B, A, D, E, F, G, I, J, H, C)D．(B, C, D, A, E, F, I, J, G, H)
