Final answer:
FAA Regulation Part 121 discusses alcohol service guidelines for airlines. It ensures airlines adhere to safety and federal laws. The other options address regulations for different types of aviation operations.
Step-by-step explanation:
The regulation that discusses alcohol and how to adhere to service guidelines for airlines is FAA Regulation Part 121. This part of the Federal Aviation Regulations (FAR) applies to most commercial airlines and covers a wide array of operational issues, including serving alcoholic beverages on board. It provides specific guidelines for alcohol service to ensure safety and compliance with federal laws.
Options 2, 3, and 4, namely FAA Regulation Part 135, FAA Regulation Part 91, and FAA Regulation Part 125 also contain regulations pertinent to aviation; however, they pertain to different aspects or types of operations. FAA Regulation Part 135 applies to commuter and on-demand operations, Part 91 is for general aviation, and Part 125 applies to operations of large airplanes not engaged in common carriage.