How can a rider determine the need to enrich the fuel mixture when starting a cold engine?

Answer: D — Utilize the choke control

When starting a cold engine, the fuel mixture may need to be enriched in order to help the engine start more easily. Option A, checking the rearview mirror, is not relevant to determining the need for an enriched fuel mixture. Option B, listening for the horn, is also not relevant and may even distract the rider from the task at hand. Option C, inspecting the tires, has no relation to the engine starting process. Option D, utilizing the choke control, is the correct answer as it allows the rider to adjust the amount of fuel being mixed with air to facilitate easier starting.