男军人参照发型有哪几种？
参考答案：
青年型、奔放型、刚健型、稳健型。
先根次序周游树等同于按哪一种方法周游二叉树
A．前序法
B．后序法
C．对称序法
D．后根次序
In the early 1960s, the famous Swiss psychologist Piaget established his theory of ______ development.
