Correct answer: A). Must rely on other means than photosynthesis
It is because the life below the water body relies on other means other than the photosynthesis. As there are a variety of life forms found which are dependent on photosynthesis but there are also some animals and plants that are not dependent on photosynthesis for food. As the sunlight cannot reach to the bottom layer with that much intensity in which photosynthesis can take place, so they must rely on other sources in order to survive.