Final Answer:
To investigate the percentage of abuse, the appropriate subject would be "b) Substances."
Step-by-step explanation:
When investigating the percentage of abuse, the context suggests focusing on the object or entity being abused. In this case, "Substances" (Option B) is the relevant category, as it pertains to the misuse or maltreatment of various substances, such as drugs or chemicals. This choice aligns with the common understanding of abuse in the context of substances rather than people, animals, or open-ended categories. The specificity of the term "Substances" makes it a suitable and direct choice for addressing the intended investigation.
Understanding the context and clarifying the type of abuse under investigation is crucial for selecting the appropriate option in this scenario.
Option B is the answer.