Step 1: Understanding the Question:
• The question asks us to arrange the factors that mainly determine speed, in order of importance.
Step 2: Detailed Explanation:
• As per the NTA final answer key, the order is: A. morphology (structure) of muscle fibres, B. regulating process of the nervous system, C. muscular strength, D. psychic factors.
• The muscle fibre structure and the nervous system's regulation are the basic physiological determinants of speed, followed by strength and psychic factors.
Step 3: Final Answer:
The correct option is (A) A, B, C, D.