Intense and reactive infants become unusually anxious and aroused when facing new or strange situations. this best illustrates the importance of

a. the x chromosome.
b. temperament.
c. epigenetics.
d. individualism.

Temperament

Explanation:

In psychology, the term temperament refers to the part of the personality that comes from our genes, we are born with some innate traits. That's why some infants and babies are really calmed and friendly while others seem more anxious or negative. In other words, the word  temperament refers to when we call a baby an "easy" or "difficult" one.

In this example, intense and reactive infants become unusually anxious and aroused when facing new or strange situations. This best illustrates the importance of temperament. Since they are infants that are manifesting some specific personality traits.