What are the two primary parts of a strand of human hair?

The correct answer identifies the two primary parts of a strand of human hair: the hair root and the hair shaft. The hair root is the portion of the hair that is embedded in the hair follicle, located beneath the skin's surface. It is essential for the growth of the hair and contains the living cells that produce the hair strand. The hair shaft, on the other hand, is the visible part of the hair that extends above the scalp. This part is composed of dead keratinized cells and is what we typically see and style.

By distinguishing between the root, which is crucial for the hair's growth and health, and the shaft, which reflects the hair's external properties, this understanding emphasizes the structure and function of hair in its entirety. The other options, while mentioning components important to hair, do not accurately identify the two main parts of a hair strand. For example, the hair follicle is associated with the root but is not part of the strand itself, and terms like hair cuticle, papilla, and cortex refer to layers and functions rather than the primary structural divisions.