Final answer:
The correct answer is B) 42 inches. The OSHA standard height requirement for guardrails in a general industry setting is 42 inches, allowing a tolerance of plus or minus 3 inches for safety reasons.
Step-by-step explanation:
The top rail of a guardrail system must be within plus or minus 3 inches of 42 inches in height. According to safety regulations, specifically those from the Occupational Safety and Health Administration (OSHA), the standard height for guardrails in a general industry setting is 42 inches, with a permissible tolerance of plus or minus 3 inches. This is to ensure the safety of workers and to prevent falls from work platforms, runways, or other elevated work areas.