GMAT Sentence Correction (SC) | Re: The adopted use of trained fighter horses

C.Adopting the use of trained fighter horses, dated by some historians at around a specific era thousands of years ago, was a critical element to the flourishment many civilizations including the Ottoman Empire

D.The adoption of using trained fighter horses, thought by some historians to have occurred around a specific era thousands of years ago, was a critical element to the flourishment many civilizations including the Ottoman Empire.

IMO Answer choice C fits better D.
In answer choice C,
...

---