Final Answer:
The purpose of allusions is to provide a greater context or meaning to the text (Option D).
Step-by-step explanation:
Allusions are literary devices where a writer refers to a person, place, event, or another piece of literature, often assuming that the reader will understand the reference and its implications. The primary purpose of allusions is to enrich the text by connecting it to broader cultural, historical, or literary contexts. While allusions may indirectly support the text (Option A) by enhancing understanding, they go beyond mere illustration, explanation, or comparison. Allusions add depth, layers, and additional meaning to the text, creating a bridge between the author's work and the broader cultural and literary heritage.
Option D is the answer.