What does this function do$?$

int FunNodes $($Node node$)1$

if $($node $==$ null$)$

return $0$ ;

else if $(($node$.$ left $==$ null && node.right $!=$ null$)$ II

$($node$.$ left $$ null && node.right $==$ null$))$

return $1+$ FunNodes $($node: node.left$)+$

FunNodes $($node: node.right$)$ ;

else

return FunNodes $($node: node. left$)+$

FunNodes $($node: node.right$)$ ;

A$.$ It counts the number of internal nodes in the tree.

B$.$ It counts the number of internal nodes with two children in the tree.

C$.$ It counts the number of internal nodes with one child in the tree.

D$.$ It counts the number of leaf nodes in the tree.