Final answer:
Mental health disorders are complex diseases involving issues with thinking, mood, and social interaction, significantly impacting quality of life and are not easily cured.
Step-by-step explanation:
The question, "Mental health disorders are __________," is asking to identify the nature of mental health disorders. The most accurate option here is C, 'complex diseases.' Mental health disorders are indeed complex diseases that involve a range of issues affecting thinking, mood, or the ability to relate to others, and they can significantly impact a person's quality of life. These disorders are multifaceted, often requiring a combination of medications, therapy, and other treatments to manage, and are not easily cured. While they may be influenced by genetic factors, life experiences, or environmental factors, mental illnesses are not typically caused solely by birth defects. It is also important to understand that mental health disorders are very much classified as diseases, contrary to option B, and have serious implications for those affected.