For gas piping installations, which of the following is an acceptable joining method for polyethylene...

This item appears to use older or simplified exam wording . Current ICC language for polyethylene plastic piping identifies heat-fusion joints, electrofusion joints, and stab-type insert fittings as the named PE joining methods, not solvent cement or threaded couplings. Among the answer choices you provided, D. Compression coupling is the only choice that aligns most closely with a mechanical fitting/joining approach for PE systems, while rubber cement, solvent cement, and threaded coupling do not match ICC PE joining practice. Because of that, D is the best answer from the listed options, but this question should be tied to the exact code cycle or source exam bank if you want absolute cycle-specific certainty