prep 07版 SC 39题关于it的指代问题，求助

onlylee0302

这道题正确答案是C，关于as is the case with看了破解上面的解释后懂了。但是，后半句没划线部分的it，指代的是什么呢？
助于不是prescriptions么，后面不应该是they么。。。
求NN们指教~~~

39. (26492-!-item-!-188;#058&003168)

As it is with traditional pharmacies,on-line drugstores rely on prescriptions to be successful, since it

is primarily prescriptions that attractthe customers, who then also buy other health-related items.

(A) As it is with traditional pharmacies,on-line drugstores rely on prescriptions to be successful

(B) As with the case of traditionalpharmacies, on-line drugstores rely on prescriptions to have

success

(C) As is the case with traditionalpharmacies, prescriptions are the cornerstone of a successful

on-line drugstore

(D) As traditional pharmacies, so on-linedrugstores rely on prescriptions to be successful

(E) Like traditional pharmacies, thecornerstone of a successful on-line drugstore is prescriptions

板栗在奋斗

嗯，楼上正解……

bejamin1111

我看it is..that是强调结构