A fielder pulls his hands back gradually with the moving ball while holding a catch. Why does he do this?

The correct option is A It reduces the impact of catching the fast moving ball.
While catching a fast moving cricket ball, a fielder in the ground gradually pulls back his hand back with the moving ball. In doing so, he experiences a smaller force for a longer interval of time to catch the ball, resulting in a lesser impulse on his hands and hence it will not hurt the hands of the fielder.