Which body parts are classified as 'yang'?

The classification of body parts into 'yang' is rooted in traditional Chinese medicine, where 'yang' represents active, outward, and hot aspects compared to 'yin', which embodies passive, inward, and cool characteristics. The surface of the body, including the skin and areas that interact with the environment, is generally considered 'yang' because these areas are exposed and engage actively with external factors.

Key viscera, particularly those involved in processes that require significant energy and activity, are also classified as 'yang'. This includes organs such as the heart and lungs, which play critical roles in circulation and respiration—essential functions that reflect the dynamic, energetic qualities of 'yang'.

In contrast, organs and body parts described in the other options tend to align more with 'yin' categories, which are associated more with internal, deeper, and less active components. Therefore, the correct answer emphasizes the outward and dynamic nature of 'yang' components, elucidating the active characteristics associated with these body parts.