"Not all of the snakes were dangerous." this means _________.

A．none of the snakes were dangerous

B．all of the snakes were not dangerous

C．few of the snakes were dangerous

D．no snakes were dangerous

采用了（）协议的以太网中，工作站在发送数据之前，要检查网络是否空闲，只有在网络不阻塞时，工作站才能发送数据。

A、TCP

B、IP

C、ICMP

D、CSMA/CD