关于编码有下述说法：  

①对字符集进行编码时，如果字符集中任一字符的编码都是其它字符的编码的前缀，则称这种编码称为前缀编码。  

②对字符集进行编码时，要求字符集中任一字符的编码都不是其它字符的编码的后缀，这种编码称为后缀编码。  

③不存在既是前缀编码又是后缀编码的编码。  

④哈夫曼编码属于前缀编码。  

⑤哈夫曼编码属于后缀编码。  

⑥哈夫曼编码对应的哈夫曼树是正则二叉树。

其中正确的是(13)。

(72)

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XP is (71) of interesting twists that encourage one to think--for example, how about "Test and then code"? I've worked with software companies and a few IT organizations in (72) programmer performance was measured on lines of code delivered and testing was measured on defects found-- (73) side was motivated to reduce the number of defects prior to testing. XP uses two types of testing: unit and functional. (74) , the practice for unit testing involves developing the test for the feature prior to writing the code and further states that the tests should be automated. Once the code is written, it is immediately (75) to the test suite bringing instant feedback.

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MPEG-4是(53)，MPEG-4主要由音频编码、视频编码、数据平面、(54)、缓冲区管理和实时识别等部分构成，其中数据平面包括(55)两部分。

(64)

(63)