15. Once the economic and social usefulness of the motor car was demonstrated and with its superiority to the horse being proved, much of the early hostility to it in rural regions disappeared.

(A) and with its superiority to the horse being

(B) and its superiority over the horse had been

(C) and its superiority to the horse

(D) its superiority over the horse（C）

(E) with its superiority to the horse having been

这题在论坛上没有搜到讨论，不知是否太简单，但是从大全注释中看到正确选项C的解释是省略了和and前面一样的谓语动词was，但是这样的省略可以吗？不是说只有当前后主谓都一致时才可以一起省略的吗？

费解

但是这样的省略可以吗？不是说只有当前后主谓都一致时才可以一起省略的吗？

I am not sure where you got that from but was indeed can be omitted here.