A vertical sluice gate, 2.5m wide and weighing 500 kg is held in position due to horizontal force of water on one side and associated friction force. When the water level drops down to 2m above the bottom of the gate, the gate just starts sliding down. The coefficient of friction between the gate and the supporting structure is
(a) 0.20 (b) 0.10
(c) 0.05 (d) 0.02