I can understand how my incorrect option fits better with convertible, but given the options for "vehicle", what I chose was certainly viable.
Your answer: a car that has top that can be folded or removed
a car that has top that can be folded or removed is the definition for "convertible"
The correct answer was a conveyance that transports people or objects
It is certainly easy to see "vehicle" as the question, and "a car" as the first two words of an incorrect answer and choose that one.