White blood cells work as: A) A defense against disease B) To produce blood C) To take messages D) None of these Related MCQs: X and Y can do a piece of work in 20 days and 12 days respectively. X started the work alone, and then after 4 days, Y joined him until the completion of the work. How long did the work last? The blood vessels that take oxygenated blood from the heart to the body are called? The lifespan of White Blood Cells is ……. day(s)? The lifespan of Red Blood cells is —–days