2024 CO CDL Practice Test: All - Test 3 Based on 2024 CO CDL Handbook 9. The dummy couplers prevent ____ and _____ entering into the coupler and the air lines. A Air; Water B Gas; Water C Dirt; Gas D Dirt; Water Next More 9/29 Progress 0 Errors Restart Next Next All - Test 3 Back to Test List All - Test 2 Tank and Hazmat - Test Challenge Library 12 More CO CDL Practice Tests 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 47 Bus - Test 3