Only fat-soluble vitamins can accumulate in an oily tissue like the liver, which immediately rules out the water-soluble vitamin C and vitamin B. Between the fat-soluble candidates, shark liver oil is specifically renowned as a rich natural source of vitamin A (alongside vitamin D and squalene), which is why it has traditionally been used to treat vitamin A deficiency and support eye and immune health. So the answer is Vit A.
We can also cross-check this against other well-known liver oils and their standard vitamin content.
Following the same pattern seen in other well-known liver oils confirms that shark liver oil's standout vitamin is vitamin A.
Therefore, the correct answer is Vit A.