AThe balance factor of each node falls within [-1, 1] 每个节点的平衡因子的绝对值不超过1
BIt is a balanced binary search tree 是平衡二叉搜索树
CThe search time is O(lgn) 支持O(lgn)时间的查找
DThe topology changes no more than O(1) after each insertion/deletion
每次插入/删除后拓扑结构的变化不超过O(1)