Answer :
Final answer:
Plastic pipe, tubing, and fittings used to supply fuel gas should be marked with the standards NSF 14 and ASTM D1785.
Explanation:
The correct answer is c) NSF 14, ASTM D1785. Plastic pipe, tubing, and fittings used to supply fuel gas should be marked with the standards NSF 14 and ASTM D1785. These standards ensure that the materials used are suitable and safe for fuel gas distribution.
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