(71) is a one -way function that takes an arbitrarily long piece of plaintext and from it computes a fixed-length bit string.
(72) is a protocol that most USENET machines now use it to allow news articles to propagate from one machine to another over a reliable connection.
(73) is an approach preferred by cable TV providers. In this solution the fiber terminates at an optoelectrical converter and the final segment is a shared coaxial cable.
(74) is a device used to connect two separate network that use different communication protocol.
(75) is a digital-to-digital polar encoding method in which the signal level is always either positive or negative.

A．Router

B．Gateway

C．Bridge

D．hub

离心泵启动前应打开出口阀，关闭入口阀。