请教语法达人一道题（出自白勇语法）

yogurthan

31. As the etchedlines on computer memory chips have become thinner and the chips’ circuitsmore complex, both the power of the chips and the electronic devices they drivehave vastly increased.
(A) the chips’circuits more complex, both the power of the chips and the electronic devicesthey drive have
(B) the chips’circuits more complex, the power of both the chips and the electronic devicesthey drive has
(C) the chips’circuits are more complex, both the power of the chips and the electronicdevices they drive has
(D) their circuitsare more complex, the power of both the chips and the electronic devices theydrive have
(E) their circuitsmore complex, both the power of the chips and the electronic devices they drivehave
这道题的解释是两个句子并列，第一个句子含有be动词或become，第二个句子中的be动词或become必须省略，所以选B
18. Once theeconomic and social usefulness of the motor car was demonstrated and withits superiority to the horse being proved, much of the early hostility toit in rural regions disappeared.
(A) and with itssuperiority to the horse being

(B) and itssuperiority over the horse had been
(C) and itssuperiority to the horse

(D) itssuperiority over the horse
(E) with itssuperiority to the horse having been
这道题选B，请问为什么不是选C，并列结构省略was呢？

yogurthan

呜呜，有木有解答一下啊