设根节点的层次为0，则高度为k的二叉树的最大节点数______。
A．2k
B．2k-1
C．2k+1
D．2k+1-1
参考答案：D
某夏，厦门受台风影响，吹偏北风；此时台风中心位于它的[ ]
A、东侧
B、西侧
C、南侧
D、北侧
It is the second time that he has won the race, _______ has surprised us all.
A．which
B．where
C．what
D．that
