Among the choices above, it is only the "pathogens" that enter the body in order to multiply and can cause infectious disease or illness to humans. Pathogens refer to <u><em>disease-causing microorganisms</em></u>. These organisms include<em> bacteria, virus, fungi, worms, etc. </em>
Phagocytes, antibodies and T cells do not enter the body because they're already inside the body. <em> Phagocytes </em>and<em> T cells</em> are natural cells within the body while<em> antibodies</em> are proteins inside the human body. The phagocytes can be found in the <em>bone marrow, connective tissue. bone tissue, etc.</em> while the<u> T-cells are part of the immune system</u>.
