根据下面的文字资料回答 72～76 题
（ 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．
第6题：文中（ 1 ）处正确的答案是（ ）。
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