Final answer:
Edgar Linton attempts to extend an invitation to Heathcliff to drink tea, representing a symbol of upper-class civility at the time.
Step-by-step explanation:
When Heathcliff returns to Thrushcross Grange as an adult in Emily Brontë's Wuthering Heights, the intent of Edgar Linton is to integrate him into the upper-class society. The correct answer to the question is that Edgar tries to invite Heathcliff to partake in a customary upper-class activity which is to drink tea. This event exemplifies a customary form of upper-class civility of the time, emphasizing the cultural gap between Heathcliff's rough upbringing and Edgar's genteel lifestyle.