Final answer:
The three principal parts of a pin curl include the base, the stem, and the circle, which are responsible for the attachment to the scalp, the direction and the movement, and the form of the curls, respectively.
Step-by-step explanation:
The three principal parts of a pin curl are: a. Base, stem, and circle. The base is the section of the hair that is attached to the scalp, the stem is the section of the curl between the base and the first turn of the curl that provides the direction and movement of the curl, and the circle is the hair that is formed into the actual curls or waves.
The three principal parts of a pin curl are the base, stem, and curl. The base is the stationary part of the curl that sits close to the scalp, providing the anchor for the curl. The stem is the section of the hair between the base and the curl. The curl is the end of the hair that creates the desired shape of the curl.
Therefore answer is a. Base, stem, and circle.