Which is not a basilica-plan structure?

Old Saint Peter's

Sant'Apollinare Nuovo

Santa Costanza

Santa Sabina

The 3rd one is correct

Option C. Santa Costanza is not a basilica-plan structure.

Explanation:

A basilica is the most common architectural style for Christian churches. The basilica-plan structure consists of a rectangular building with a central nave and aisles, and usually a raised platform at the opposite end from the door. While Old Saint Peter's, Sant'Apollinare Nuovo and Santa Sabina are all basilicas, Santa Costanza is not. Santa Costanza is a church built during the 4th century in the city of Rome. The church is a circular, centralized structure topped by a shallow dome which is raised on a round drum.