求助：As it is with...的问题

39.  As it is with traditional pharmacies, on-line drugstores rely on prescriptions to be successful, since it is primarily prescriptions that attract the 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 traditional pharmacies, on-line drugstores rely on prescriptions to have success

(C) As is the case with traditional pharmacies, prescriptions are the cornerstone of a successful on-line drugstore

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

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

 一般说As应该后面跟一个句子，这里B，C选项的As with the case of... 和As is the case with... 都不是一个句子，如果按照逻辑意思应该就把C，E杀掉了，为什么答案给的是C啊？？？As it is with...应该是一个句子对吗？

请牛人们多多指点