1. Arteries : Carry's blood away from the heart.
2. Veins : Carry's blood back to the heart.
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3. Capillaries : exchange of materials and gases between the cell and vessel takes place here.</span>
One carbon atom has 4 valence electrons. Hope this helps
Yes! A recent example could be babies that do not survive child birth for a certain reason, are obviously unable to pass on whatever caused them to die in the first place.
Also, once humans started to domesticate cows and drink their milk (I'm not sure why humans drink a cow's milk) their bodies evolved to continue making the enzyme to digest milk even after they were weaned off their mothers milk. Many people of Asian descend do not have this enzyme, since their culture did/does not raise as much dairy product.
