算子网，请指点一下

问题描述：

Which three IP addresses can be assigned to hosts if the subnet mask is /27 and subnet zero is usable? (Choose three.)

A. 10.15.32.17

B. 17.15.66.128

C. 66.55.128.1

D. 135.1.64.34

E. 129.33.192.192

F. 192.168.5.63

是怎么算的，希望详细点，谢谢
看不懂啊，指点一下吧

问题解答：

the subnet mask is /27
你先搞懂掩码的意义
然后就懂了。