金属油罐的阻火器、呼吸阀、量油孔、人孔、透光孔等金属附件必须保持（）连接。
参考答案：等电位
，原来制作透明板的材料是[ ]
A.金属材料
B.天然纤维
C.合成材料
D.天然橡胶
We are lucky to be among the generation of people who have________and experienced the great social
changes in our country.[ ]
A. reported
B. appreciated
C. impressed
D. witnessed
，原来制作透明板的材料是[ ]