For pre-school age, guardrails greater than 20 inches but less or equal to 30 inches must have a total height of:

For pre-school age, guardrails must have a total height of 20-30 inches. Option A, 29 inches, falls within this range, making it the correct answer. Option B, 38 inches, is greater than 30 inches and therefore outside of the specified range. Option C, 23 inches, is less than 20 inches and also outside of the specified range. Option D, 9 inches, is significantly less than the required height of 20 inches and would not provide adequate safety for pre-school age children. Therefore, option A is the best choice.