实验室有三瓶失去标签的试剂，分别是Na₂CO₃、NaCl、AgNO₃，实验员选择了一种试剂就把它们区别开来了，这种试剂是（  ）

阅读短文，从A，B，C，D四个选项中，选出可以填入空白处的最佳选项。

    What do you do after class at your school? You may say you go 1 and do 2 homework. But I think we can have 3 other things to do after class.

    We can 4 different clubs, like the art club and the music club. What can you do? If you swim well, you 5 in the swimming club. Maybe(也许) you can't play the violin 6 the guitar well, but you can 7 to play them at the music club. 8, some people there can help you. I like books and I often go to the 9 club. Do you like books? Come 10 me.