(A) of being dwellings that must also operate as businesses

(B) of dwellings that must also operate like business

(C) that they are dwellings that must operate like business

(D) that, as dwellings, they must also operate like businesses

(E) to be a dwelling that must also operate as a business

这个题A和D不能区分出来。谁能给我解释一下A的用法，以及D为什么错了。