单项选择题
Each NCS woks as a type of（）, assisting controlling and monitoring telex and telephone network as quickly as possible.
A.switch operator B.communication gateway C.national operator D.on-scene commande
单项选择题 The position of the AOR-W satellite in the INMARSAT system is（）above the equator.
单项选择题 Geostationary satellite are artificial satellite which（）.
单项选择题 A radio link between a transmitting earth station and a receiving earth station through one satellite is named a（）.
