The adopted use of trained fighter horses, which some historians date around a specific era thousands of years ago, was a critical element to the flourishment many civilizations including the Ottoman Empire.

(A) The adopted use of trained fighter horses, which some historians date
(B) The adopted use of trained fighter horses, which some historians have thought to occur
(C) Adopting the use of trained fighter horses, dated by some historians at
(D) The adoption of using trained fighter horses, thought by some historians to have occurred
(E) The trained fighter horse's adopted use, dated by some historians to have been