题目内容：
根据下列题干，回答题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 itcomputes 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 communicationprotocol.
(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
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