For each blank, choose the best answer from the four choices and write down on the answer sheet.
(1) is a one-way function that takes an arbitrarily long piece of plaintext and from it computes a fixed-length bit string.
(2) 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.
(3) 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.
(4) is a device used to connect two separate network that use different communication protocol.
(5) is a digital-to-digital polar encoding method in which the signal level is always either positive or negative.
4（）
A．Router
B．Gateway
C．Bridge
D．Hub
