Within the polar areas it is（）to see a satellite in geo-stationary orbit .

A.climate
B.sunshine
C.human beings
D.both a and b

A.One means, whether satellite or terrestrial techniques
B.Two means, whether satellite or terrestrial techniques
C.Two separate and independent means, each using different radio communication services
D.Two means, such as MF DSC and HF DSC

A.all large passenger vessels
B.freighters of more than 300gt in coastal waters
C.all passenger ships and cargo ships engaged in international-voyages
D.all passenger ships and cargo ships of 300gt upwards in open sea