题目内容：
根据下列题干，回答题：（ 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 optoelectricalconverter 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．
请选择（1）处最佳答案：
参考答案：
答案解析：