SC TOUGH from 1000 sc

[hritik]

"The domesticated camel, which some scholars date" around the twelfth century B.C., was the key to the development of the spice trade in the ancient world.
(A) The domesticated camel, which some scholars date
(B) The domesticated camel, which some scholars having thought to occur
(C) Domesticating the camel, dated by some scholars at
(D) The domestication of the camel, thought by some scholars to have occurred
(E) The camel's domestication, dated by some scholars to have been

[GmatKiss]

"The domesticated camel, which some scholars date" around the twelfth century B.C., was the key to the development of the spice trade in the ancient world.
(A) The domesticated camel, which some scholars date
(B) The domesticated camel, which some scholars having thought to occur
(C) Domesticating the camel, dated by some scholars at
(D) The domestication of the camel, thought by some scholars to have occurred
(E) The camel's domestication, dated by some scholars to have been

will go for D

[kdraj]

"The domesticated camel, which some scholars date" around the twelfth century B.C., was the key to the development of the spice trade in the ancient world.
(A) The domesticated camel, which some scholars date -> means Domesticated Camel was the key ....
(B) The domesticated camel, which some scholars having thought to occur -> means Domesticated Camel was the key ....
(C) Domesticating the camel, dated by some scholars at -> Domesticating should be in a past tense
(D) The domestication of the camel, thought by some scholars to have occurred -> Correct because the process is thought to be the key
(E) The camel's domestication, dated by some scholars to have been->to have been around 12th - idiomatically wrong.

[sl750]

IMO, A

The subject is the domesticated camel, because it would be illogical to say that the domestication led to the development of spice trade

In D, it uses the present perfect have occurred, but the non underlined verb is in the simple past tense ,was

[vishwas.arora]

"The domesticated camel, which some scholars date" around the twelfth century B.C., was the key to the development of the spice trade in the ancient world.
(A) The domesticated camel, which some scholars date
(B) The domesticated camel, which some scholars having thought to occur
(C) Domesticating the camel, dated by some scholars at
(D) The domestication of the camel, thought by some scholars to have occurred
(E) The camel's domestication, dated by some scholars to have been

Should be D.

What is the OA?