Question

find the relative clause. if it is nonrestrictive, set it off with commas. if it is restrictive, submit the text without making any changes. when adding organic materials to a compost pile, gardeners should avoid animal products and fats in favor of scraps from plants that have not been treated with pesticides.

Explanation:

The relative clause "that have not been treated with pesticides" is restrictive as it defines which plant - scraps gardeners should use. Restrictive clauses are not set off with commas.

Answer:

When adding organic materials to a compost pile, gardeners should avoid animal products and fats in favor of scraps from plants that have not been treated with pesticides.