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:

A relative clause starts with a relative pronoun (like "that", "which", "who", etc.) and modifies a noun. Here, the noun "plants" is modified by the clause "that have not been treated with pesticides". This is a restrictive relative clause because it provides essential information about which "plants" we're referring to (the ones not treated with pesticides), so we don't set it off with commas.

Answer:

that have not been treated with pesticides