Final answer:
The correct answer is C, which states that concave perm rods lead to a larger, looser curl on the hair wrapped around the center of the rod, due to the variable diameter of the rod affecting the hair's curl size.
Step-by-step explanation:
With concave perm rods, the hair on both ends travels farther to make one complete turn around the rod than the hair in the center. This creates a larger, looser curl on hair wrapped around the center of the rod, and a tighter curl at the ends. This effect is due to the geometry of the concave rod; as the diameter changes, so does the circumference that the hair wraps around, which in turn affects the size of the curl. The center of the rod has a larger diameter, leading to a greater circumference, therefore, hair in this section will have a looser curl.
The process of creating perms involves chemicals that break down the hair's structure, allowing it to be reformed around the rods. Once the chemicals are neutralized, the hair retains the curled form due to the formation of new chemical bonds, making this a permanent hairstyle.