The correct sentence is: "The bike on the bike rack is blue."
All other sentences contain grammatical errors. Here’s a breakdown:
- "The surface of the parking lots were redone this summer." - Should be "was" instead of "were" because "surface" is singular.
- "The sidewalks in the courtyards has been decorated with chalk." - Should be "have" instead of "has" because "sidewalks" is plural.
- "The cars in the parking lot belongs to the teachers." - Should be "belong" instead of "belongs" because "cars" is plural.