河北省环京津旅游圈主要包括哪几个地区？
参考答案：
承德，张家口，保定以及廊坊四个地区。
The new school _________ in the past five years.
A built B has been built C has built D will be built
设根结点的层次为O，则高度为k的完全二叉树的最小结点数为 ______。
