Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:
This is GMAT+ question and I wanted to check my answer. I also selected B. Because that is the closest choice that can be correct. But I do not agree that B is a correct construction. With choice B, we will have "was demonstrated and ...... had been proved". One is simple past tense and the other is past perfect. They both should have the same tense as they are being joined by "and".
The correct answer given in GMAT+ was C and I believe that the answer can not be C. The answer could be C only if the choice is changed to "and its superiority to the horse was". The word "was" is missing from choice C.
In short, there are two possibilities:
(1) There is a typo in choice C (do not know if that is possible) OR
(2) B is the answer even with the lack of parallelism in tense.