For $$3 \times 3$$ matrices M and N, whichof the following statement(s) is (are) NOT correct ?

A

$$N^T M N$$ is symmetric or skew symmetric, according as M is symmetric or skew symmetric

B

M N - N M is skew symmetric for all symmetric matrices M and N

C

M N is symmetric for all symmetric matrices M and N

D

(adj M) (adj N) = adj (M N) for all invertible matrices and N