一定条件下，在一个密闭容器内发生某反应，测得反应前后各物质的质量如图所示．

下列关于以上反应的说法中，正确的是（　　）

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单词的正确形式填空
    Do you know how to be a top student? Top students are decided by a new way now. New rules for middle school students ____ (come) out in March. The best students should not only have good grades. You'll be a top student ____  you follow the new rules.____  (one), you need to be honest. You should never copy others’ homework. Second, good students love animals and care____ other people. They try to do something to protect animals, too. Are you one of them? Third, you should learn that teamwork____  important. So be friendly to the people you are with and it can make your team stronger.