Correct Answer: (A) Residual volume increases

Step 1 - What long-term effects mean:

Long-term effects are the permanent changes that appear in the body after regular training over a long period, and they are seen even when the person is at rest.

Step 2 - Long-term effects on the respiratory system:

The size of the lungs and chest increases, tidal volume and vital capacity increase, residual volume increases, unused alveoli become active, endurance improves and the rate of respiration at rest actually decreases.

Step 3 - Why the others are wrong:

An increase in respiratory rate and in the rate of gaseous exchange are immediate or short-term effects that occur during exercise itself. Stroke volume belongs to the circulatory system, not the respiratory system.

Hence, option (A) is correct.