The correct answer is the following.
Replace one common noun with a proper noun of your choice. Identify your replacements with (P) for “proper” and (C) for “common.”
"Day after day after day, Jefferson street and the park in the city stood deserted. Sid, my sister, and I stayed in shady corners and in front of old plastic fans that twisted back and forth, back and forth."
What I did was to replace the common noun main street for the proper noun Jefferson street, and the proper noun "Midville" for the common noun "city."
In Grammatics, a common noun refers to general concepts: a street, a name. On the other hand, proper noun names specific places or people.