一道困扰我n久的SC,请NN帮忙开个窍

白勇大全上的，估计大家也比较熟的一道题，不过我马上要考试了，还是不知道正确答案到底应该选哪个

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.

B. and its superiority over the horse had been

C. and its superiority to the horse

答案选B，我一直觉得选C

C的这句话也是很多语法书里作为第二个be动词省略的例子，白勇的书里也有拿这个解释省略。我觉得也很顺。

但是正确答案选B, 我觉得从语法上来说也是对的，毕竟had been proved发生在disappeared之前，也比较妥当。

但是考虑到与was demonstrated对称以及省略，我还是觉得C应该是最佳选项。

马上考试了，这道题一直没搞明白，郁闷之极，恳请高手指教下。