The correct answer isDbecausequality assuranceis the function that focuses on giving confidence that the required level of quality will be achieved through planned and systematic activities. It is preventive in nature.
Rather than waiting for defects to appear and then detecting or correcting them, quality assurance establishes the framework of procedures, controls, audits, document management, qualification practices, and surveillance methods that help ensure the work is done correctly from the start.
By contrast,quality controlis more directly associated withdetectionof defects and nonconformities through inspection, examination, and testing of the product or process output.Inspectionis one part of quality control, not the broader confidence-building system.Quality planningis the activity of defining what standards, resources, acceptance criteria, and methods will be used, but it is not itself the ongoing function primarily described in the question.
In API-aligned source inspection practice, the inspector works within a quality system that relies on both assurance and control. However, when the emphasis is onproviding confidence that quality requirements will be fulfilled, the correct term isquality assurance, makingoption Dthe best answer.