Final answer:
Edgar Lee Masters is best known for his work in poetry, specifically the "Spoon River Anthology," which provides a candid look at small-town life through poetic epitaphs.
Step-by-step explanation:
Edgar Lee Masters is most known for d) Writing poetry. He is particularly famous for the Spoon River Anthology, a collection of free verse poems that narrate the epitaphs of residents in a fictional small town called Spoon River. This work uncovers the hidden and often scandalous stories of the inhabitants from their own perspectives, posthumously speaking from the grave. It's considered a landmark in American literature for its frank portrayal of small-town life and its innovative use of monologue.