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The answer is :
D. The formation of a receptor-ligand complex.
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Answer:
A scientific theory is a well-substantiated explanation of some aspect of the natural world, based on a body of facts that have been repeatedly confirmed through observation and experiment. Such fact-supported theories are not "guesses" but reliable accounts of the real world.
Explanation:
Well, A humans brain is bigger than a Sheeps brain, And a human has more Ridges and Contours also, Hope this helps