接地系统按功能分为哪几种?有何关系?
参考答案:接地系统按功能来分有三种,即工作接地、保护接地、防雷接地。目前这三种接地方式倾向于采用一组接地体,该接地体方式成为联合接地。
肠道血吸虫病,一般不发生
A.肠黏膜息肉B.肠黏膜虫卵结节形成C.肠壁增厚、肠腔狭窄D.肠出血、肠穿孔E.肠黏膜溃疡
-How much are the pants?
-_____[ ]
A. It's black.
B. It's 20 yuan.
C. They are 80 $.
D. They're red.