Question $39(3$ points$)$

After $3$ values $30,20,$ and $10$ are inserted into an empty AVL tree, what action is

needed to maintain the AVL tree?

double rotation, with the right rotation at $20,$ left rotation at node $30$

a single rotation to the left at node $30$

double rotation, with the left rotation at $20,$ right rotation at node $30$

a single rotation to the right at node $30$