Which of the following best describes herbicides?

Herbicides are specifically designed to control unwanted plants or weeds. They work by inhibiting the growth of these plants, effectively reducing competition for resources like nutrients, water, and sunlight that desired crops need. This targeted mechanism is what categorizes herbicides uniquely from other types of pesticides, which serve different purposes.

While some terms are associated with herbicides, like fungicides for fungi or insecticides for pests, herbicides focus solely on the eradication or management of weeds. Thus, option C is the accurate description of what herbicides do, highlighting their primary function in agriculture and land management.