FIXED: Uncaught TypeError: Cannot call method 'off' of undefined
articleopr.js:1061
暂时修复：从书中获取到的句子的个数与用户跟读的句子的个数不同，程序错误！！！ SentencesPlayer.js:116
     voicesLength=18, sentencesLengthFromBook=9, _sentences.length=18
     这个错误。