Concept:White blood cells are scientifically known by a specific medical term derived from their colour and cell structure.Explanation:White blood cells are called leucocytes, from the Greek words leukos (white) and kytos (cell).Erythrocytes are red blood cells, not white blood cells.Lymphocytes and phagocytes are specialised types of white blood cells, but they are not the overall name for all white blood cells.Therefore, the general term for white blood cells is leucocytes.Answer:B. Leucocytes.