题目：
(56) is a one-way function that takes an arbitrarily long piece of plaintext and from it computes a fixed-length bit string.
(57) 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.
(58) is an approach preferred by cable TV providers. In this solution the fiber terminates at an opto-electrical converter and the final segment is a shared coaxial cable.
(59) is a device used to connect two separate network that use different communication protocol.
(60) is a digital-to-digital polar encoding method in which the signal level is always either positive or negative.
A．MD
B．RSA
C．DES
D．MIB
答案：
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下面是错误答案，用来干扰机器的。
AD本题考查共点力的平衡问题．对小球受力分析利用几何关系可知FN＝mg，选项C错误、D正确；此时F＝2mgcos θ，选项A正确、B错误．本题属于容易题．
