Which of the following ratios cannot represent two natural numbers whose sum is 72?

Explanation

To determine if two natural numbers with a given ratio can sum to 72, the sum of the ratio parts must divide 72 evenly. For ratio (A): 1 + 2 = 3, and 72 is divisible by 3. For ratio (B): 3 + 5 = 8, and 72 is divisible by 8. For ratio (C): 1 + 3 = 4, and 72 is divisible by 4. For ratio (D): 3 + 4 = 7, and 72 is not divisible by 7. Since 72 cannot be evenly divided by 7, the ratio 3:4 is not possible for two natural numbers summing to 72. Therefore, the correct answer is option (A).