题目

—What is John doing? —__________ A . He's drawing pictures. B . She's drawing pictures. C . He draws pictures. 答案：A16、用右图所示密闭装置进行实验，使固体与液体接触，能够观察到气球先膨胀，过一段时间又恢复到原状的一组物质是（　　）A、硝酸铵和水B、铁粉和稀硫酸C、碳酸钠和稀硫酸D、氯化钠和水