<h2>
Answer</h2>
It is because of different arrangements of nucleotide bases.
<h2>
Explanation</h2>
There are only five types of nucleotide basis are present in the genetic material which makes up the all the genetic information of the individuals. These nucleotides are named as Adenine, Thymine, Guanine, Cytosine and Uracil. In all the living beings on the earth, these only five nucleotides are present which decides their behaviour and functions on the earth. These five bases have features to get any arrangements according to the situation. Their different arrangement at the heredity material makes the difference in all living beings regarding their behaviour.
Cory is reluctant to leave her home and attend college despite just being finished with her teenage years. Usually, the people of this age are explorative and are trying to find their identity in the world separately, but Cory seems to stay isolated even from Mike, which indicates that she might be going through the stage of stress. Stress makes a person to avoid any kind of interaction with other people and inhibits the urge to explore the life outside one's comfort zone. So, Cory is going through the stress stage.