What color is the service air line on a combination vehicle?

a.Red

b.Blue

c.Green

d.Yellow

Explanation

The service air line is blue. It carries air controlled by the foot brake or the trailer hand valve to operate the trailer brakes.

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About the CDL Exam

The CDL (Commercial Driver License) exam tests your knowledge of commercial driving rules, safety procedures, and vehicle operation. You must score 80% or higher to pass the written knowledge test. The exam covers general knowledge, air brakes, combination vehicles, and various endorsements.

This question is from the CDL Combination Test #1 section. Practice with more questions from this category to build confidence before taking the official DMV test.

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