Final answer:
At a minimum, a street-legal bike should have one headlight and possibly two side mirrors depending on the jurisdiction. The number of gears or wheels does not determine its street-legal status.
Step-by-step explanation:
The minimum requirements for a bike to be considered street-legal depend on local and national regulations. As a rule of thumb, a street-legal bike should at the very least have one functional headlight for visibility during low-light environments (option A). In some jurisdictions, two side mirrors may also be required to provide the rider with adequate field of vision for safety (option B). The number of gears (option C) and the number of wheels (option D) do not determine street-legal status. Always consult your local traffic rules to ensure your bike is street-legal and safe to ride.
Learn more about Street-legal Bike Requirements