The adopted use of trained fighter horses, which some historians date during early Ottoman rule, was a critical element to the expansion of 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
(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