Answer:
The correct answer is option b, that is, the mouth.
Step-by-step explanation:
The diminished penetration of light is a result of the murkiness of water because of the enormous deposits of sediments. The sediments getting gathered at the water moves towards the mouth of the streams and mouth, making the water to get muddy and murky, and thus becomes impossible for light to pass through. Thus, because of diminished light penetration, the mouth of the streams and rivers will exhibit less diversity of plant life.