$1.$ Which of the following is a logical equivalence in first$-$order logic?

A$.($x$)$P$($x$)($x$)$P$($x$)$

B$.($x$)($y$)$P$($x$,$ y$)($y$)($x$)$P$($x$,$ y$)$

C$.($x$)($P$($x$)->$ Q$($x$))($x$)($P$($x$)$ Q$($x$))$

D$.($x$)($P$($x$)$ Q$($x$))($x$)($P$($x$)$ Q$($x$))$