题目

把你的妈妈介绍给同学们，你会说：________ A . This is my father. B . This is my mother. C . He is my mother. 答案：B写出下列装置或测量工具所依据的物理原理．（1）锅炉水位计：______；（2）发电机：______；（3）水银温度计：______；（4）托盘天平：______．