What is wrong with the getFun method? private int getFun $($Node head$)\{$if $($head $==$ null$)$return $0$;elseint length $=0$;length $=$ length $+$ getFun $($head: head. left$)$;length $=$ length $+$ getFun $($head: head.right$)$;return length A$.$ It returns one less than the actual number of nodes. B$.$ It returns the correct number of nodes.O C$.$ It returns $1,0,-1$ to calculate Balance Factor. D$.$ It always returns $0.$