Comprehensive and Detailed In-Depth Explanation:

ISO 9001:2015 emphasizes continual improvement as a fundamental requirement of an effective Quality Management System (QMS).

Clause Reference:

Clause 4.4.1 (Quality Management System and Its Processes) states that organizations must:

Determine processes needed for the QMS

Establish criteria and methods for process effectiveness

Ensure continual improvement of the system

Why is the Correct Answer C?

Continual improvement is a core principle of ISO 9001.

Organizations must regularly assess and enhance their QMS to adapt to new challenges and maintain effectiveness.

Why are the Other Options Incorrect?

A (To change the QMS quarterly) → ISO 9001 does not mandate a specific frequency for system changes.

B (To review the QMS annually) → QMS reviews must be conducted as needed, not strictly annually.

D (To conduct a QMS gap analysis every two years) → Gap analysis is useful but is not a mandatory requirement under Clause 4.4.