prep1-87,句子结构题,特来请教大家

87. While they remove carbon dioxide from the air, conserve soil and water, and house thousands of species, forests also supply potentially valuable pharmaceuticals, and, as sources of building material and firewood, that provide employment for millions worldwide.

A. pharmaceuticals, and, as sources of building material and firewood, that provide

B. pharmaceuticals, and sources of building material and firewood, are providers of

C. pharmaceuticals and, as sources of building material and firewood that are provide

D. pharmaceuticals and as sources of building material and firewood, for providing

E. pharmaceuticals and, as sources of building material and firewood, provide

此题答案是E,我选D,因为E的话,主句有两个谓语了"SUPPLY和PROVIDE"请大家帮我解疑惑.谢谢

(E)and连接两个句子呀

(D)and （supply） for providing明显意思重复