Explanation:

- First, calculate the volume of water flowing per second. The flow rate is 2.5 km/h. Convert this to meters per minute: 2.5 km/h = 2500 m/h = 2500m/60min ˜ 41.67 m/min.

- The cross-sectional area of the river is width × depth = 35 m × 6 m = 210 m².

- Volume of water flowing per minute = cross-sectional area × speed = 210 m² × 41.67 m/min = 8750 m³/min.

- Option 4: 8750 m³ is the correct amount of water running into the sea per minute.

- Correct Answer: Option 4 – 8750 m³