Why is there a border between light and dark on the moon

As the Moon orbits around the Earth, we are able to see more or less of the half that is illuminated. ... There is a border between light and dark on the moon because the sun illuminates the half of the moon that is facing it. Leaving the other half dark.

Explanation:

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b - the respond is innate and varies over time.

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enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products