(A) The domesticated sheep of 8,000 years ago were
quite dissimilar from the wild sheep of the
time. >> Weakens the conclusion. So not an assumption.

(B) There are no other existing breeds of sheep that
escaped from domestication at about the
same time as the forebears of the mouflon.
>> Not related to the passage. Passage talks only about Mouflon sheep.

(C) Modern domesticated sheep are direct descen-
dants of sheep that were wild 8,000 years ago.
>> This statement is incorrect as the passage indicates modern domesticated sheep are produced after deliberate selective breeding.
(D) Mouflon sheep are more similar to their fore-
bears of 8,000 years ago than modern domes-
ticated sheep are to theirs.
>> This is the assumption that conclusion depends on. This assumption binds the following together
1. Wild Mouflon sheep --direct descendants AND 2. so mouflon sheep can provide picture of what their forebears look like.

(E) The climate of Corsica has not changed at all in
the last 8,000 years.
>> Passage does not talk about climate and this is not relevant for conclusion.