The correct answer is A. Erythrocytes.
Erythrocytes are red blood cells that carry oxygen from the lungs to the rest of the body. They are also responsible for removing carbon dioxide from the body. Erythrocytes are made in the bone marrow and have a lifespan of about 120 days.
B. Leucocytes, also known as white blood cells, are cells of the immune system that fight infection. They are produced in the bone marrow and lymph nodes. There are five types of leucocytes: neutrophils, lymphocytes, monocytes, eosinophils, and basophils.
C. Thrombocytes, also known as platelets, are cell fragments that help the blood to clot. They are produced in the bone marrow.
D. Eosinophils are a type of white blood cell that helps the body fight infection. They are also involved in allergic reactions.