Quality Assurance in this context refers to

• A. The daily QA supervisor's role on site
• B. The cost-control review at project completion
• C. The contractor's internal quality checks
• D. The verification process through which QC test results are verified, with random sampling at greater intervals; Buyer's responsibility.

Answer: (D)

Quality assurance is the process that ensures the credibility of testing results by verifying them, often through independent checks and a structured sampling plan. It isn’t about performing the tests itself; it’s about confirming that the QC data are accurate and representative before they’re used to make decisions about acceptance or payment. In this context, random sampling helps prevent bias and provides a fair check across the project, and the Buyer carries responsibility for this verification framework.

The other descriptions describe activities that aren’t the verification-focused, cross-checking role of QA: on-site supervision details the day-to-day management of QA activities, cost-control reviews focus on budgeting rather than data validity, and the contractor’s internal quality checks are QC activities rather than the verification process that QA provides.