They have a certain shape of active sites which only fit in certain substrates
See lock and key theoru
The exceptions to this rule are the pulmonary arteries and veins.
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The pulmonary artery is the one that carries deoxygenated blood from the right side of the heart (ventricle) to the lungs. On the other side, pulmonary veins transfer oxygenated blood from the lungs to the heart (left atrium).</span>
Equation B has all 4 quantities.
I'm thinking it might be fossil evidence. Hope it helps!