Which part of your body allows you to keep control of the ATV, including braking ability?

The best choice in this scenario pertains to the function that your arms perform while operating an ATV. Your arms are essential for steering and handling the handlebars, which directly relates to your ability to control the vehicle's direction and maintain stability. Additionally, your hands are crucial for operating the brake levers, allowing you to slow down or stop the ATV effectively.

In contrast, the other options do not directly contribute to the control of the ATV. While hand strength is important for gripping and operating controls, it does not encompass the full scope of control like the overall function of your arms. Foot length may play a role in fitting the ATV's foot controls, but it does not actively contribute to control or braking. Leg coordination is also significant for balance and stance but is secondary to the primary actions performed by your arms while operating the ATV. Thus, the arms play the most significant role in maintaining control and ensuring safety while riding an ATV.