Answer:
C. complex diseases.
Explanation:
Mental health illness are often called disorders, which have a huge complexity, you can notice this by simply reading the fact that experts don't know if classify them as actual disease nowadays, but they are mental affections no doubts.
The reality around mental illness is that researches are hard to manage because the patterns that make mental illness appear is wide. The fact that we cannot see this kind of illness make them really hard to diagnose and treat, most of the cases medications just drug the person to having them into a "suspended" state.
