Final answer:
A pesticide is typically a substance used to kill or manage pests. Insecticide, a category of pesticide, is the most direct answer to the question, as it is specifically designed to kill insects.
Step-by-step explanation:
A pesticide is a substance used to kill, repel, or control certain forms of plant or animal life that are considered to be pests. Pesticides include various categories, such as insecticides, which are specifically designed to kill insects; herbicides, which target unwanted plants or weeds; and insect repellents, which do not kill insects but rather deter them from approaching an area. Although bleach can be used as a disinfectant to kill germs, it is generally not classified as a pesticide for controlling pests like insects or weeds. The most direct answer to the question 'A pesticide could be:' is b. Insecticide, which specifically refers to a chemical or substance that kills insects, one of the functional categories of pesticides.