求助pp23兩個觀念

[Superjenny]

23. (25773-!-item-!-188;#058&002128)

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 providing
(D) pharmaceuticals and sources of building material and firewood, for providing
(E) pharmaceuticals and, as sources of building material and firewood, provide

我有選到正確答案
但我想確認一下我的結構觀念
D. 我無法解釋for providing..........的結構所以D的結構錯誤錯吧?
E.的as sources of building material and firewood式個插入句
我該怎麼翻他? as當介詞是表身分 可是在這裡不通.

[Superjenny]

More than all the North American Great Lakes combined, Siberia's Lake Baikal, with more than 300 rivers draining into it, holds 20 percent of the world's fresh water. 順便請問一下這句是不是也是流水句?
感恩

[raist]

選項D把"sources of building material and firewood"由插入句提上來，改變了句意。

選項E的as應該可以翻譯為"做為"，詞性是介詞沒錯。

"More than all the North American Great Lakes combined, Siberia's Lake Baikal, with more than 300 rivers draining into it, holds 20 percent of the world's fresh water."文法應該可以，但句意已與原句有相當大的差異，因此不可選。