Blood

by Read Listen Learn · Science · Upper-Intermediate

Until recently, blood was simply blood. But we have discovered different blood types and that can literally save our lives when we need transfusions. All blood can be categorised as Rhesus positive or negative, but we don’t know why. We also know nothing about why human beings have four blood types but cows have 800. This article explores the mysteries of blood. (865 words).

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