The correct answer is option 4) i.e. To highlight that it is twice as large as the great white shark. Explanation
From the second last sentence of the passage "The Blue Whale is the largest known mammal to ever live" we can say that Blue whale is the largest creature on land and sea.
The mammal is any of a class of warm-blooded higher vertebrates (such as placentals, marsupials, or monotremes) that nourish their young with milk secreted by mammary glands, have the skin usually more or less covered with hair, and include humans.
Hence, "It is the largest creature on land and sea" is the correct answer.