2024 CO CDL Practice Test: All - Test 2 Based on 2024 CO CDL Handbook 11. The dummy couplers prevent ____ and _____ entering into the coupler and the air lines. A Dirt; Gas B Dirt; Water C Air; Water D Gas; Water Next More 11/29 Progress 0 Errors Restart Next Next All - Test 2 Back to Test List All - Test All - Test 3 Challenge Library 12 More CO CDL Practice Tests 37 All - Test 3 38 Tank and Hazmat - Test 39 Tank and Hazmat - Test 2 40 Class C - Test 41 Class C - Test 2 42 Class C - Test 3 43 Class C - Test 4 44 Class C - Test 5 45 Bus - Test 46 Bus - Test 2