Please note:
The correct idioms are:
X date Y at....... --OR--
Y is dated by X at.....Both forms are correct. There is no problem with "dated by".
The trap is that
there is no "at" in the non-underlined part.
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
Wrong. "which" is not the main problem. The
"Of-phrase" makes the phrase "of trained fighter horses" a
"mission-critical" <== Thus, "which" does not need to modify the preceding noun (horses). "which" in this case can modify "the adopted use".
But
A is wrong because there is no preposition "at" after "date" ==> The structure is like historian date during early Ottoman rule. Sounds badly!
(B) The adopted use of trained fighter horses, which some historians have thought to occur
Wrong. Meaning problem. "the USE of trained fighter horses" cannot occur, only "the adoption of using" can occur. (
logical problem)
(C) Adopting the use of trained fighter horses, dated by some historians
Wrong. Same as A.
We need the preposition "at".
(D) The adoption of using trained fighter horses, thought by some historians to have occurred
Correct. Even though D is wordy, but it's correct.
(E) The trained fighter horse's adopted use, dated by some historians
Wrong. The possessive structure is very awkward. In addition,
We need the preposition "at".Hope it helps.
.
If wrong please correct me thanks, But IMO, I think the word 'adopting' is not correct because the activity happened in the past and no longer continued at present.