One-third of the area covered with trees. About seventy percent of the trees been plant

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A. is; has
(答案→)B. is; have
C. are; have
D. are; has
解析：考查主谓一致：当主语被分数或百分数修饰时，谓语和后面的名词一致，第一空One-third of +单数名词+单数谓语，第二空seventy percent of +复数名词+复数谓语，句意：三分之一的地区被绿树覆盖。已经种植了大约百分之七十的树木。选B。