**Core Concept**
The World Health Organization (WHO) defines health as a state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity. This definition encompasses multiple dimensions of health, which are crucial for overall well-being.

**Why the Correct Answer is Right**
The WHO definition of health includes physical, mental, and social dimensions. The physical dimension refers to the body's physiological functioning, while the mental dimension encompasses cognitive, emotional, and behavioral aspects. The social dimension involves relationships, social connections, and community involvement. These three dimensions are essential for achieving overall health and well-being.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not explicitly mentioned in the WHO definition. The definition focuses on physical, mental, and social dimensions, but does not include spiritual or environmental dimensions.
* **Option B:** While mental health is indeed included in the WHO definition, there is no mention of spiritual health. However, this is not the correct answer as it is a part of the definition.
* **Option C:** This option is not included in the WHO definition. The definition focuses on individual health, but does not specifically mention environmental health.
* **Option D:** This option is not included in the WHO definition. The definition focuses on individual health, but does not specifically mention economic health.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the WHO definition of health is a broad concept that encompasses multiple dimensions, including physical, mental, and social well-being. This definition serves as a guiding principle for healthcare professionals and policymakers to promote overall health and well-being.

**Correct Answer:** A