Which statement regarding red-black trees is wrong? 以下关于红黑树的说法，错误的是：
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A．A red-black tree of size n has a balck height of O(lgn), but the height is not necessarily O(lgn)含n个节点的红黑树，其黑高度为O(lgn)，但是总的高度却未必是O(lgn)
B．There cannot be two consecutive red nodes in a path from a external node to the root从红黑树的任一外部节点上溯到根节点，沿途不可能经过连续两个红色节点
C．The black height cannot be smaller than half the height红黑树的黑高度一定不小于总高度的一半
D．x (black) and y (black) are two children of a black node. The black height of the sub-trees x and y must equal.红黑树中的黑色节点u有黑色左孩子x和黑色右孩子y,则x与y的黑高度一定相等