Analysis of the program's logic:
The program prints "YES" if the condition (s < 5) and (t > 5) is true. Otherwise, it prints "NO". Let's check each pair:
- 1) (2, 7): s = 2, t = 7. Condition: (2 < 5) is true, and (7 > 5) is true. Both are true, so the output is "YES".
- 2) (6, 9): s = 6, t = 9. Condition: (6 < 5) is false. The overall condition is false, so the output is "NO".
- 3) (4, 8): s = 4, t = 8. Condition: (4 < 5) is true, and (8 > 5) is true. Both are true, so the output is "YES".
- 4) (5, 7): s = 5, t = 7. Condition: (5 < 5) is false. The overall condition is false, so the output is "NO".
- 5) (-1, 5): s = -1, t = 5. Condition: (-1 < 5) is true, but (5 > 5) is false. The overall condition is false, so the output is "NO".
The pairs for which the program prints "YES" are (2, 7) and (4, 8). These correspond to options 1 and 3.
The question asks to write the numbers of the selected pairs in ascending order.
Answer: 1, 3