Final answer:
Precursors refer to 1) Substances that can be chemically altered to make a controlled substance.
Step-by-step explanation:
Precursors refer to substances that can be chemically altered or transformed to produce a controlled substance. These substances serve as the starting materials for the synthesis or production of drugs. In the context of drug manufacturing, precursors are often used to create illegal substances, such as methamphetamine or ecstasy, by undergoing chemical reactions or modifications.
For example, pseudoephedrine, which is found in certain cold and allergy medications, can be chemically altered to produce methamphetamine, an illegal and highly addictive drug. The correct answer is 1) Substances that can be chemically altered to make a controlled substance.