Final answer:
A decrease in sediment size in a river typically indicates a decrease in the river's gradient, as a wider channel and slower current promote sedimentation. correct option is B
Step-by-step explanation:
The question relates to the effects of a river's gradient on the size of sediments it carries. A decrease in the size of sediments carried by a river usually reflects a decrease in the gradient of the river. When a river flows away from its source, it often widens and the current slows down due to a decrease in gradient and an increase in volume from joining tributaries, resulting in more sedimentation.