阅读下面短文，按照句子结构的语法性和上下文连贯的要求，在空格处填入一个适当的词或使用括号中词语的正确形式填空，并将答案填写在答题卡标号为16—25的相应位置上。  In order to know a foreign language thoroughly, four things are necessary. Firstly, we must understand the language when we hear    16.          spoken. Secondly, we must be able to speak it ourselves correctly with confidence and without hesitation.    17.               , we must be able to read the language, and fourthly, we must be able to write it. We must be able to make sentences that are grammatically correct.

There is no easy way to success   18.           language learning.          19.                   good memory is a great help, but it is not enough only    20.                  (memorize) rules from a grammar book. It is not much use learning by heart long lists of words and   21.                meanings, studying the dictionary and so on. We must learn by using the language. 22           .        we are satisfied with only a few rules we have memorized, we are not really learning the language. “Learn through use” is a good piece of   23.           (advise) for those   24.          are studying a new language. Practice is important. We must practise speaking and   25.           (write) the language whenever we can.

操作人员不得佩戴戒指是对食品加工人员的个人卫生要求之一。( )