The correct option is C the
'The' is the correct option, because the noun it is used for, Iliad, is an epic, well known by most scholars. There's only one epic in the world with the title 'Iliad' and hence it's correct. Options A and B are incorrect because indefinite articles are used for nouns which are not specified, whereas here the noun is specified. Option D is incorrect because, though articles are not required in front of proper nouns, there are exceptions when it comes to extraordinary works of art, ones which are unique to the world.