Which of these statements are true?

Multiple select question.

If f$1($x$)$ is O$($g$($x$))$ and f$2($x$)$ is O$($g$($x$))$ then, $($f$1+$ f$2)($x$)$ is O$($g$($x$)).$

If f$1($x$)$ is O$($g$1($x$))$ and f$2($x$)$ is O$($g$2($x$))$ then, $($f$1+$ f$2)($x$)$ is O$($max$(|$g$1($x$)|,|$g$2($x$)|)).$

If f$1($x$)$ is O$($g$1($x$))$ and f$2($x$)$ is O$($g$2($x$))$ then, $($f$1+$ f$2)($x$)$ is O$($min$(|$g$1($x$)|,|$g$2($x$)|)).$

If f$1($x$)$ is O$($g$($x$))$ and f$2($x$)$ is O$($g$($x$))$ then, $($f$1$ f$2)($x$)$ is O$($g$($x$)2).$