Final answer:
Residual nuclear fragments in red blood cells are represented by Pappenheimer bodies, which are remnants of undegraded cell organelles.
Step-by-step explanation:
The residual nuclear fragments being asked about in the student's question refer to Pappenheimer bodies. These are small, basophilic, iron-containing granules that can be found in red blood cells and are visible on a stained blood smear under a microscope. They represent remnants of cell organelles that have not been completely degraded during the maturation process of erythrocytes. In contrast, Cabot rings are ring-like structures occasionally seen in red blood cells, Heinz bodies are agglomerates of denatured hemoglobin caused by oxidative damage, and the repeated option, Pappenheimer bodies, stays the correct choice among those provided.