The factor which does NOT influence the size of the workforce is ______.

A．a population growth from natural increase leads to a greater proportion of the work force
B．a large population does not necessarily mean a higher proportion of work force
C．the larger the number of the aged in a population, the higher the proportion of the work force
D．if the population has an evenly spread age distribution, the work force will be lower

A．people who are available to work and earn income
B．self-employed people only
C．only those who are looking for an employment
D．only the employees