In a Business Context, What Is the Best Definition of Personal

In a business context, what is the best definition of personal space?

A) It is the amount of distance to be maintained from the audience in order to be audible to them.
B) It is a psychological phase wherein a person has free flowing thoughts.
C) In ergonomics, it is the minimum amount of space required by an average employee in order to work efficiently.
D) It is the comfortable amount of distance between you and someone you are talking with.
E) It is the amount of space a country has per person and is arrived at by dividing the country's total geographical area by its total population.