电容器按结构的不同可以分为（）。
A.固定电容器
B.可变电容器
C.微调电容器
D.陶瓷电容器
参考答案：A, B, C
开机前，对空气输送斜槽应作哪些项目的检查？
From the ___ expression on her face, we knew that the problem was ____.
A．puzzling….puzzling
B．puzzled…puzzled
C．puzzling..puzzled
D．puzzled..puzzling
