Why is the meeting with Hades important to the
development of the theme?

(D) because Hades is convinced of Orpheus’s love and grants him his wish

Explanation:

Theme in literature are used to entertain, to teach a moral lesson, to convey meaning, or more importantly, to make the reader aware of some aspect of the human condition. The writers creatively share their ideas and express themes that are timeless and universal.  

The meeting with Hades is the way the writer develops the theme with a specific purpose. The purpose is by meeting with Orpheus, Hades gives him the opportunity to realize his wish, which was to return Orpheus's wife, Eurydice, into the world of the living. This meeting creates the setting for what  the tragedy that is to come.

true. the definition explains it: a word or phrase that modifies or qualifies an adjective, verb, or other adverb or a word group, expressing a relation of place, time, circumstance, manner, cause, degree, etc. this is a dictionary definition that i have looked up in a dictionary.