IP报文的第三个字段是()。

Sorry sir, we don't have wine or beer. We are only licensed to sell _______ drinks.

D类IP地址的前导码是()。

The student found the novel _______. It provided him with so much information about the subject.

A baby might show fear of an unfamiliar adult, _______ he is likely to smile and reach out to another infant.

PPP帧的数据长度是可变的，默认字节值是()。

Internet上从服务器到服务器传递邮件的协议是()。

最基本的Internet服务是不可靠的，是因为它并不保证正确的传输()。

TCP协议在两台计算机之间提供可靠的()。

________ with the size of the whole earth, the highest mountains do not seem high at all.