(b) 4000 m³
Distance covered in 2 min = $2000 \times \dfrac{2}{60} = \dfrac{200}{3}$ m. Volume = $3 \times 40 \times \dfrac{200}{3} = 8000$ m³.
Wait — recalculating: distance = $2 \text{ km/h} \times \dfrac{2}{60} \text{ h} = \dfrac{2}{15} \text{ km} = \dfrac{200}{3}$ m.
Volume $= 3 \times 40 \times \dfrac{200}{3} = 8000$ m³. → (c) 8000 m³
The river cross-section acts as the base (depth × width = 3 × 40 = 120 m²). In 2 minutes at 2 km/h, water travels $2000 × \frac{2}{60} = \frac{200}{3}$ m. Volume = 120 × 200/3 = 8000 m³. Option (c) is correct. A common mistake is forgetting to convert km/h to m/min before multiplying.