Modern communications satellites use a variety of orbits, including ( ). A: geostationary orbits B: Molniya orbits C: elliptical orbits D: low (Polar and non-polar) earth orbits

Geostationary satellites are the man-made satellites which . A: are always fixed in the regular position B: sometimes move with the earth C: are synchronizing with the movement of the earth D: can not fly off from the ground

Unlike the American GPS, Russian GLONASS, and European Galileo systems, which use median Earth orbit satellites, BeiDou-1 uses satellites in （ ）. A: Geostationary orbit B: Circular orbit C: Sun-synchronous orbit D: Near polar orbit

()service means a service which is based on polar orbiting satellites which receive and relay distressalerts from satellite EPIRBs and which provides their position . A: Geostationary satellite B: Near-polar orbiting satellite C: synchomizing satellite D. D: Terrestrial satellite

______ is sea area A2. A: An area within coverage of INMARSAT geostationary satellites B: An area, excluding sea area A1, within coverage of Medium Frequency (MF) coastal radio stations in which continuous DSC alerting is available C: An area within coverage of VHF coast radio stations in which continuous DSC alerting is available D: The extreme polar regions