请教白勇语法全解page 132, #18

Once the economic and social helpfulness of the motor car was demenstrated and with the superiority to the horse being proved, much of the early hosility 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

E) with its superiority over the horse having been

Answer: B

请教两个问题：

1）answer C. 白勇的排除理由是and连接once从句和its superiority短语，两者形式不对称。我的疑问是C为什么不对。我的理解是and连接the economic...从句和its superiority to the horse (was) proved? was省略因为and前面句子有一个was.

2) answer B. and后面的句子the horse had been用过去完成时，为什么and前面的demenstrate用一般过去时而不用过去完成时？

谢谢！

1）answer C. 白勇的排除理由是and连接once从句和its superiority短语，两者形式不对称。我的疑问是C为什么不对。我的理解是and连接the economic...从句和its superiority to the horse (was) proved? was省略因为and前面句子有一个was.

句子的结构是：Once the economic and social helpfulness of the motor car was demonstrated and its superiority over the horse had been proved... 两个独立的句子不能共享谓语的！

2) answer B. and后面的句子the horse had been用过去完成时，为什么and前面的demenstrate用一般过去时而不用过去完成时？

个人认为这里demonstrate用过去完成时或用过去时都可以，prove也一样。