A.The ocean covers 71 percent of the earth’s surface and it is a basic component of the global bio-support system. B.The ocean, which covers 71 percent of the earth’s surface, is a basic component of the global bio-support system. C.F100ding 71 percent of the earth’s surface, the ocean forms a basic component of the global bio-support system, D.The ocean, which is a basic component of the global bio-support system,covers 71 percent of the earth’s surface.