Are all fungi producers?

No. Fungi are decomposers.  A producer, makes its own food. A fungus does not make its own food, it breaks down nutrients from dead organisms to get a part of what it needs to survive. Which is why it is called a decomposer.

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affects the water bodies: excessive use of fertilizers causes eutrophication. the fertilizers which are used on plants affect the quality of land on which it is used, further causing erosion of soil. the fertilizers used on plants contain harmful chemical fumes which affect the environment.

age range would be the answer