Explanation:

- A car moves uniformly at 72 km/h.

- This translates to 20 meters per second (since 72 km/h = 72000 meters per hour ÷ 3600 seconds per hour).

- It takes 18 seconds to travel from the 1st to the 10th pole.

- In 18 seconds, the car covers 360 meters (18 seconds × 20 meters per second).

- The distance from the 1st to the 10th pole spans 9 gaps, as there are 9 intervals between 10 poles.

- This means each gap is 40 meters long (360 meters ÷ 9).

- The distance from the 10th to the 31st pole includes 21 gaps (since there are 31 - 10 = 21 intervals).

- The distance between the 10th and 31st pole is therefore 840 meters (21 gaps × 40 meters each).

The correct answer:

Option 3: 840