A. 地区监控中心 B. 局站监控中心 C. 区域监控中心 D. 传感器中心 E. 设备监控单元
A. 正确 B. 错误
A. a single mast B. two masts: with the mizzen stepped abaft the rudder post C. two masts: with the mizzen stepped forward of the rudder post D. at least two masts: a foremast and a mainmast