All of the following involve organizations that are exempt from income tax under Section $501($c$)(3).$ Which is an example of an unrelated business activity for an exempt organization?

Let's Read!, Inc., a literacy program, conducts a bake sale, which is run by the volunteers, every month.

Charity Medical Clinic, Inc, a small medical facility located in a rural area, has an onsite cafeteria for the convenience of the medical personnel and patients.

The Heroes Project, Inc, an organization to provide shelter for homeless veterans, operates a thrift store that sells donated goods.

The Puppy People, Inc., an animal welfare organization, operates an ice cream stand in a food court throughout the year. The ice cream stand is staffed by paid employees.