No covered employee can report for duty with an alcohol concentration of _____ or greater.

The correct answer is based on the regulations set forth by the Federal Aviation Administration (FAA) concerning the allowable alcohol concentration for covered employees in aviation. Specifically, under 14 CFR Part 120, which outlines the alcohol misuse prevention program, no covered employee may report for duty or perform safety-sensitive functions with an alcohol concentration of 0.04 or greater.

This regulation is in place to ensure safety in the aviation industry, recognizing that even low levels of alcohol can impair judgment and performance. The threshold of 0.04 is significant because it facilitates the identification and prevention of potential impairment among employees in critical roles that affect flight safety.

This regulatory framework is in the interest of maintaining a safe environment for both passengers and crew members. Various other thresholds mentioned in the options do not align with the federal standard set for aviation, which is strictly enforced to promote accountability and safety within the industry.