Answer:
a) cocktail party effect
Explanation:
Cocktail part effect: In psychology, the concept of cocktail party effect refers to the phenomenon of an individual's brain capacity to focus on his or her auditory attention related to a specific stimulus by neglecting out the range of various other stimuli.
Example: A man is present in a party playing high music can easily talk to another person by focusing on the person's sound and neglecting the sound of music as well as that of another person.