Question

which answer choice is a complete sentence?
fixing a car by himself in the garage.
opened the store at noon.
the parade was cancelled.
if the rainstorm.

Explanation:

A complete sentence has a subject and a predicate. "Fixing a car by himself in the garage" is a gerund - phrase, lacking a subject doing the action. "Opened the store at noon" is missing a subject. "If the rainstorm" is an incomplete conditional phrase. "The parade was cancelled" has a subject "the parade" and a predicate "was cancelled".

Answer:

The parade was cancelled.