单选题：Let's traverse a complete binary tree in level-order, and define

Let's traverse a complete binary tree in level-order, and define the level-order index of the root to be 1. Then for the $$i$$-th node visited, if its right child exists, then the index of this right child is___.
@[C](3)

A. $$2i$$
B. $$i+2$$
C. $$2 i + 1$$
D. $$2 ( i + 1) +1$$



A.$$2i$$
B.$$i+2$$
C.$$2 i + 1$$
D.$$2 ( i + 1) +1$$


答案：C