Which of the following is a key reason to include allusions in a literary work?
a)to create new insights and ideas by associating unexpectedly similar objects
b)to explore humans’ relationships to ideals, inner lives, and environments
c)to broaden the context and deepen the meaning of a literary work
d)to equate a known object with an unknown or to-be-explained object

Option C is correct.

To broaden the context and deepen the meaning of a literary work is a key reason to include allusions in a literary work.

in our power to make a world happy - to teach mankind the art of being so - to a character hitherto unknown - and to have, as it were, a new creation intrusted to our hands, are honors that command reflection, and can neither be too highly estimated,