Final answer:
When a tennis ball rolls onto the road, you should touch the brakes and prepare to slow down, responding immediately but without abrupt actions that could endanger yourself or others.
Step-by-step explanation:
If a tennis ball rolls onto the road ahead of you while driving vehicle A, the correct action to take is C. Touch the brakes and prepare to slow down. This response ensures that you are ready to react and slow your vehicle if necessary, while avoiding abrupt actions that could cause you to lose control of your vehicle or create a hazard for other road users. Swerving suddenly or braking hard can be dangerous and should be avoided unless absolutely necessary. It's important always to stay alert and react immediately but calmly to unexpected obstacles on the road.