For each blank, choose the best answer from the four choices and write down on the answer sheet.
(66) is a one-way function that takes an arbitrarily long piece of plaintext and from it computes a fixed-length bit string.
(67) 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.
(68) 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.
(69) is a device used to connect two separate network that use different communication protocol.
(70) is a digital-to-digital polar encoding method in which the signal level is always either positive or negative.

A．ADSL

B．FITC

C．HFC

D．FTTH

气相色谱法分析空气中TVOC所用氮气，纯度应不小于（）。

A.99%

B.99.9%

C.99.99%

D.99.999%