Answer: The correct answer is "Stranger Anxiety".
Explanation: Stranger anxiety can be understood as a form of distress that a child experiences when he/she is exposed to a person or group of persons he/she is not familiar with (A stranger). Most children experience stranger anxiety, so it is widely considered a normal or a typical part of the developmental process.
In this particular case, Baby Polly is demonstrating stranger anxiety because she is usually a calm happy baby when she is around her parents and siblings but as soon as her parents take her to a reunion where there are unfamiliar people her behavior changes as a sign of evident distress.