What critical caution must a truck driver exercise when using a powerful Retarder (continuous brake) on slippery, wet, or snow-covered roads?

1. The retarder may only be used when the transmission is in reverse
2. The retarder will extinguish the headlights
3. Retarders cause tires to freeze solid
4. Because the retarder acts exclusively on the driven axle(s), excessive retarder braking torque on low-friction pavement can lock the drive wheels and cause an immediate jackknife or oversteer skid; reduce retarder stages or disengage on slippery surfaces