Which of the following statements describe(s) the properties of a purely segmented memory systemⅠ．It divides memory into units of equal sizeⅡ．It permits implementation of virtual memoryⅢ．It suffers from internal fragmentation

A．Traversing the forest corresponding to the binary tree in root-first order.
B．Traversing the forest corresponding to the binary tree in root-last order.
C．Traversing the forest corresponding to the binary tree in breadth-first order.
D．None of the abovE.

A．Ⅰ和Ⅱ
B．Ⅰ、Ⅱ和Ⅲ
C．Ⅱ和Ⅳ
D．Ⅱ、Ⅲ和Ⅳ