[求助]大全43题，as的用法

43.1.            According to Booker T. Whatley’s recent analysis, planting the same crops as are planted on large farms will lead to economic disaster for the small farmer, who should plan a succession of high-value crops that will provide a year-round cash flow.

(A) planting the same crops as are planted on large farms will lead to economic disaster for the small farmer, who

(B) it will lead to economic disaster for the small farmer to plant the same crops as on the large farms; they

(C) economic disaster will result from planting the same crops as large farms to
                    the small farmer, who

(D) economic disaster for the small farmer will result from planting the same crops as on the large farms; they

(E) the small farmer planting the same crops as are planted on large farms will lead to economic disaster; they

选项A正确，这个as是什么用法呢？？ 我只知道as+助动词+主语或者as+主语+助动词表示与什么什么一样。这里前面是planting，as后面是are planted，完全对不上啊。。。。。

"as" here is used as a pron.

I will give you an explaination and some example tommorrow.