单选题Which of the following is equipment provided by the telephone company that provides remotediagnostic and loopback services for subscriber lines?（）A 66 blockB DemarcC Smart jackD 110 block
题目
单选题
Which of the following is equipment provided by the telephone company that provides remotediagnostic and loopback services for subscriber lines?（）
A
66 block
B
Demarc
C
Smart jack
D
110 block