Final answer:
Adding loose pieces of hair to cornrows primarily creates additional volume, enhancing the fullness of the hairstyle. The key effect is on the volume, not shine, straightness, or texture.
Step-by-step explanation:
When adding loose pieces of hair to cornrows, it can create additional volume and fullness to the hairstyle. Cornrows are a style of braiding and by incorporating extra hair, you can make each braid appear thicker and more pronounced, which results in a voluminous look. Although adding hair might slightly alter the shine and texture, the primary effect is on the volume of the cornrows. This technique doesn't necessarily straighten the hair as cornrows involve braiding close to the scalp, which can be done on natural or textured hair. Therefore, the correct answer is A) Volume.