> List one area where Walmart has a monopoly and the only grocer in town.

I'd recommend you do some reading to understand the definition of a monopoly, as it pertains to pricing power: https://www.ftc.gov/advice-guidance/competition-guidance/gui...

A business doesn't need to be the literal only option for it to have monopolistic power over a market.

The Sherman Anti-Trust Act uses 50% market share as a general criteria for when a business could have monopoly power in a market. Based on that definition, here's an answer for your

> List one area where Walmart has a monopoly

Check out the table in the back of the source I linked, and you'll find 203 of them!