Explain why the function is discontinuous at the given number a$.($Select all that apply.$)$

f$($x$)=$

$1$x $+3$

$$

a $=3$

lim$$x$3$f$($x$)$ does not exist.

f$(3)$ and$$lim$$x$3$f$($x$)$ exist, but are not equal.

f$(3)$ is undefined.

lim$$x$3+$f$($x$)$ and$$lim$$x$3$f$($x$)$ exist, but are not equal.

none of the above