2024 NC CDL Practice Test: Class A - Test 5 Based on 2024 NC CDL Handbook 12. What color is the trailer air supply knob? A Yellow. B Green. C Black. D Red. Next More 12/30 Progress 0 Errors Restart Next Next Class A - Test 5 Back to Test List Class A - Test 4 Class A - Test 6 Challenge Library 12 More NC CDL Practice Tests 6 Class A - Test 6 7 Class A - Test 7 8 Class A - Test 8 9 Class B - Test 10 Class B - Test 2 11 Class B - Test 3 12 Class B - Test 4 13 Class B - Test 5 14 Class B - Test 6 15 Class B - Test 7