from space, the earth, with water seventy percent of its surface looks like a blue ball.A.

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A. Seen; covered
(答案→)B. Seen; covering
C. Seeing; covered
D. Seeing; covering
解析：
这题考查非谓语动词的用法：第一空填seen，是过去分词做状语，因为the earth和see是被动关系，第二空填covering是with复合结构，因为water和cover 是主动关系。选B。