Article 55 of the "Construction Law": If a construction project is contracted in general, the general contractor shall be responsible for the quality of the project. Where a general contractor subcontracts a construction project to other units, it shall be jointly and severally liable for the quality of the subcontracted project and the subcontractors. The subcontractor shall accept the quality management of the general contractor.

Therefore, it is A's responsibility to give correct answers, and some reference answers are wrong, Comrade.