请教一个语法点

西风瘦马

18: According to a recent survey of municipal services, the city’s streets could be cleaner, its fire code be better enforced, and its crime rate reduced if the current administration improved its management practices.

A: be better enforced, and its crime rate reduced

B: better enforced, and its crime rate reduced

C: could be better enforced, and it could reduce its crime rate

D: better enforced, and its crime rate could reduce

E: could be better enforced, and its crime rate reduce

请教NN一个语法点，被动结构的be动词是系动词还是助动词？如果是系动词，则此题应选B,如果是助动词，似乎应选A

西风瘦马

没人理。我顶，NN快来看