The answer is object permanence.
Object permanence refers to the ability to understand that an object is still present and physically exists even if it is hidden out of sight. In this example, your niece lacks object permanence since she does not understand that you are behind the blanket even though you cover yourself with it or you are temporarily.
<span>This an example of a social reinforcer. A social reinforcer shows appreciation for an individual by praising or showing happiness for an individual. This is usually done by complimenting the individual, smiling for their effort or performance or, hugging, or giving someone your attention.</span>
C Nuclear Fission is the right answer