Yong Park is nine months old. Lately when his mother tries to leave him in the church nursery, he cries and clings to his mother. His seems especially anxious if there is a new worker in the nursery. Considering his age, Yong Park is probably experiencing .

separation anxiety    

Explanation:

Separation anxiety: In psychology, the term "separation anxiety" is described as the tendency of an individual to experience excessive worry or fear related to separation from the person whom he or she is attached to or home.

Separation anxiety is considered as one of the normal stages in a child's development because it helps different children to comprehend specific relationships and therefore masters the environment to which he or she belongs to.

In the question above, Yong Park is probably experiencing separation anxiety.

the branch of biology that deals with the normal functions of living organisms and their parts.

the way in which a living organism or bodily part functions.