无线上网卡的卡托上有一个ICCID是指的什么？
参考答案：
ICCID为用户卡编码。
The Internet is an open system, and most information is available to everyone. It is very important to add ______ to existing system for protecting the secret information.
A．web pages
B．modem
C．security
D．network
一个栈的入栈序列是a，b，c，d，e，则栈不可能的输出序列是
A．e d c b a
B．d e c b a
C．d c e a b
D．a b c d e
