Final answer:
The safety of a gas line is determined by specific building codes and professional standards, which include various requirements such as material, installation, and regular maintenance. None of the given options (A, B, C, or D) are universally correct without referencing specific codes.
Step-by-step explanation:
The question regarding the safety conditions for a gas line does not correspond to a universal standard but rather to specific building codes and regulations that can vary by jurisdiction. In general, for a gas line to be considered safe for use, several conditions must be met.
These include proper material selection (e.g., black iron, HDPE), adequate wall thickness, suitable protective coatings to prevent corrosion, proper installation by a qualified professional, regular inspection and maintenance, adherence to maximum length requirements to ensure adequate gas pressure and flow, and often the implementation of shut-off valves for safety.
Without specific code references, none of the options given (A, B, C, or D) can be determined as the absolute requirement for gas line installations. Hence, it is critical to consult with local building codes and professional guidelines for the correct standards to ensure gas line safety.