If $\mathrm{A}$ and $\mathrm{B}$ are two skew symmetric matrices of the same order then $\mathrm{AB}$ is skew symmetric if and only if
(a) $\quad \mathrm{AB}+\mathrm{BA}=0$
(b) $\quad A B-B A=0$
(c) $\quad \mathrm{AB}+\mathrm{BA}=\mathrm{I}$
(d) $\quad A B-B A=I$