The correct answer is Option 2 i.e the skin to keep themselves warm [ alt="428" src="//storage.googleapis.com/tb-img/production/20/09/428.png" style=" width: 40px; height: 40px; float: left;">Explanation: Reading the above sentence we find that: Here 'keep warm' should be there in place of 'Keep themselves warm' Keep, Stop, turn, qualify, bathe, move, rest and hide do not take a reflexive pronoun after them. Example: She hid herself in the room. (wrong). She hid in the room. (right) ​Hence from the above points, we find that the mistake is in Option 2 and is, therefore, the correct answer. The correct sentence is: 'They have a layer of fat, or blubber, under the skin to keep warm in the cold water, and, other than the walrus, all species are covered in fur.'