以下关于Ethernet说法不正确的是( )。

A．在Ethernet中任何一个结点发送数据都要首先争取总线使用权

B．在Ethernet网中，若一个结点要发送数据，它将以广播方式把数据通过作为公共传输介质的总线发送出去

C．连在总线上的所有结点都能“收听”到发送结点发送的数据信号

D．结点从它准备发送数据到成功发送数据的发送等待延迟时间是确定的

In the following essay, each blank has four choices. Choose the most suitable one from the four choices and write down in the answer sheet. There are two types of key technology: private key and public key. Private-key encryption methods are called (71) ciphers, information is encrypted with (72) both the sender and receiver hold privately. Public-key encryption methods are called (73) ciphers, (74) created for each user, encryption key and decryption key are (75)

A．a key

B．two keys

C．three keys

D．four keys