What is the correct sequence of Six Sigma Process improvement approach?

The answer is A. 2, 5, 1, 4, 3, Define, Measure, Analyze, Improve, Control
Six Sigma is a disciplined, data-driven approach and methodology for eliminating defects (driving toward six standard deviations between the mean and the nearest specification limit) in any process – from manufacturing to transactional and from product to service.

In a nutshell, here are the key principles of Lean Six Sigma Business Transformation to bear in mind:
Focus on the customer.
Identify and understand how the work gets done (the value stream).
Manage, improve and smooth the process flow.
Remove Non-Value-Added steps and waste.
Manage by fact and reduce variation.

Critical to Quality (CTQ) Trees help you translate broad customer needs into specific, actionable, measurable performance requirements. You can then use these requirements to deliver high quality products and services. CTQ Trees were originally developed as part of the Six Sigma methodology.