Find the domain. f$($x$)=2/1-$x$^2$ Group of answer choices $(-$infinity, $1)$ U $(1,$ infinity$)(-$infinity, $-1)$ U $(-1,1)$ U $(1,$ infinity$)(-$infinity, $-1)$ U $(-1,$ infinity$)(-$infinity, $-1)$ U $(1,$ infinity$)$