Be和Become的省略问题.大虾帮帮忙!

想请教大家一道题. 谢谢

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

A. and with its superiority to the horse being

B. and tis superiority over the horse had been

C. and its superiority to the horse

D. its superiority over the horse

E. with its superiority to the horse having been

挣扎在B.和C

答案给的是B.  解释C的错误原因是once从句和its superiority不平行

但是C不能理解为 and its superiority to the horse (be) proved. 省略了助动词be么?

B用过去完成时是不是比较的awkward? 

谢谢大虾们帮忙! 感激不尽!

请冒出个NN为我解答一下好么.快考试了.比较急.

谢谢啦!