The correct answer is D. Green plants.
Green plants are the only organisms that can photosynthesize, which is the process of using sunlight to convert carbon dioxide and water into glucose and oxygen. This process is essential for life on Earth, as it provides the oxygen that we breathe and the food that we eat.
Fungi, protozoa, and bacteria are all heterotrophs, which means that they cannot photosynthesize and must obtain their energy from other sources. Fungi obtain their energy by breaking down organic matter, protozoa obtain their energy by eating other organisms, and bacteria obtain their energy by a variety of methods, including photosynthesis.
While heterotrophs play an important role in the ecosystem, they do not fix as much solar energy as green plants. This is because green plants are the only organisms that can use sunlight to create their own food.
In conclusion, the correct answer to the question “Maximum fixation of solar energy is done by” is D. Green plants.