What does the fun method return when the current node $($curr$)$ is null?

private Node fun $($Node curr, int min, int max$)\{$

if $($curr $==$ null$)$

return null;

curr.lChild $=$ fun $($curr$.$lChild, min, max$)$;

curr.rChild $=$ fun $($curr$.$rChild, min, max$)$;

if $($curr$.$value $<$ min$)\{$

return curr.rChild;

$\}$

if $($curr$.$value $>$ max$)\{$

return curr.lChild;

$\}$

return curr;

a$.$ The left child of the current node

b$.$ null

c$.$ The right child of the current node

d$.$ The current node itself