The construction of the two railway lines ________ by now. [ ]

A. has completed

B. have completed

C. have been completed

D. has been completed

天线对于LTE网络优化有着重要的意义，其典型的工程隐患包括（）。

A、天线接反问题

B、天线安装问题（如方向角无法调整）

C、天面阻挡问题

D、天线隔离度问题