用括号内所给词的适当形式填空。

1. —What club do you want________(join)?

    —Music club.

2. My pencil case is lost. Can you help me________(find) it?

3.—Can your sister_________(draw)?

   —Yes, she can.

4. Today is Sunday. Let's_________(play) chess.

5. I like_________(draw).I want to join the art club.

6. Mary can dance________(good).

7. I can speak_________(China).

8. Here_________(be)a card for you.

9. He wants__________(be) an actor.

10. I can see three__________(piano)  in the room.

现有硫酸镁和硫酸钠的混合物12.8g，全部溶于50g水中，加入一定量的氢氧化钠溶液，恰好完全反应生成5.8g沉淀，过滤后，所得溶液中溶质的质量分数为16.7%．试计算：

（1）原混合物中硫酸镁的质量分数；

（2）所加氢氧化钠溶液中溶质的质量分数．