安装变送器的管道，其前置直管段长度至少应为测量管内径的（）倍。
A.1
B.2
C.5
D.10
参考答案：C
―When are you going there?
―I am going there______ May, the 12th. [ ]
A. in
B. on
C. at
D. for
什么叫接户线，对接户线档距有什么规定？
