The correct answer is B) Add the Sun; the source of energy. Add a decomposer also like fungi.
The other options for the question were A) the food web is correct as is. I would not change anything. C) the food web is missing the decomposer. Bacteria of fungi can be added. D) the food web is missing the top-level consumer. A predator must be added.
What I would change this food web to make it more accurate is I would add the Sun; the source of energy. Add a decomposer also like fungi. The Sun is of the utmost importance here because it is the provider of energy and life. The Sun is the most important source of energy on planet Earth. No Sun, no life. As simple as that. It is also important to include a decomposer also like fungi because the process of decomposition is part of the cycle of nature and life. That is how new life can be formed.