Final answer:
Leukocytes, also known as white blood cells, are the type of cells that help protect the body against disease by fighting infections and eliminating pathogens. The option (D) is correct.
Step-by-step explanation:
The type of cell that helps protect against disease is the leukocyte. Leukocytes, or white blood cells, function in the body's defense system against infectious diseases and foreign invaders. While there are various types of leukocytes, including neutrophils, eosinophils, basophils, monocytes, and lymphocytes (B cells and T cells), they all play a critical role in the immune response.
Leukocytes can recognize and eliminate pathogens, fight infections, and are also involved in the healing processes. In contrast, hemoglobin is a part of red blood cells and carries oxygen, stem cells give rise to different cell types, and erythrocytes are the red blood cells that carry oxygen but do not play a direct role in immune defense. Therefore, option (D) is correct.