【Test-6-4】假设二叉树中每个结点值为单个字符， 采用二叉链存储结构存储。下面算法的功能是：求二叉树 b 中最小值的结点值。请在空白处填入正确的语句。void FindMinNode(BiTNode *b, char &min){ if (_______①________) _______②______; FindMinNode(b->lchild, min); //在左子树中找最小结点值 __________③___________; //在右子树中找最小结点值}void MinNode(BiTNode *b) //输出最小结点值{ if (b != NULL) { char ______④_______; FindMinNode(_____⑤____, min); printf("Min=%c\n", min); } }