A metric is an operational definition that describes, in very specific terms, what something is and how the quality control process measures it. A measurement is an actual value. For example, it is not enough to say that meeting the planned schedule dates is a measure of management quality. The project management team must also indicate whether every activity must start on time or only finish on time and whether individual activities will be measured or only certain deliverables and if so, which ones. Some examples of quality metrics include defect density, failure rate, availability, reliability and test coverage. In this context, quality metrics should be used during ______ (select the best answer).
A．quality assurance
B．quality planning
C．quality control
D．quality assurance, quality control