A、BECAusE Both hAvE A limitED supply oF Air, wAtEr, AnD othEr rEsourCEs.
B、BECAusE thEEArth movEs ArounD thE sun As FAst As A spACEship.
C．BECAusE wE CAn trAvEl to outEr spACE.
D．BECAusE thEEArth nEvEr stops moving.