Answer:
C. Basilica plan
Explanation:
Basilicas were the buildings where most public facilities such as courts were built in Ancient Rome.
After the Empire adopted Christianity as official religion, but more importantly, after it fell, Catholic churches began to be built following the architectural plan of basilicas, and the word basilica came to be synonymous with large catholic church.
The full name of St. Peter's is St. Peter's basilica, because of its architectural plan. It is the largest church in the world, and it's considered to be the holiest Catholic shrine.
