This sentence tells us that The Waste Land is difficult to understand, but scholars' writing can make it easier, as it does something to the meaning behind this work. We can imply that scholars' writing probably makes the meaning clearer.
The only word connected to making something clearer is (C), "elucidate." "Elucidate" means "to make clear," so it fits the blank. The other word we might be tempted to use is (E), "promote": we can promote the meaning behind poetry. It's not correct in this context, however, since promotion doesn't have anything to do with understanding the meaning.
The correct answer is (C).