Answer:
Mimicry.
Explanation:
Mimicry may be defined as the art of imitating or copying the act of someone or something. Children are most likely to imitate the other person in order to understand and entertain them.
Billy when he saws his father doing shaving, started copying his father and starts shaving. Billy behavior shoes the example of mimicry. Because he is trying to copy the act of his father. This is children psychology that like to imitate someone.
Thus, the correct answer is option (3).-