Final answer:
Duo-servo style drum brake systems have both self-energizing and servo action, resulting in improved braking performance.
Step-by-step explanation:
Duo-servo style drum brake systems have both self-energizing and servo action. This means that they have features that enhance their braking performance. Self-energizing refers to the ability of the brake shoes to create more force as they come into contact with the drum, resulting in greater braking power. Servo action refers to the use of a mechanical mechanism that multiplies the force applied to the brake shoes, making the braking process more efficient.