1. is the number of people living in a square mile. in the future, economically developed nations may not have enough money to take care of older citizens because of 2. . in low-income nations, 3. is one reason for the low standard of living.

choices are:

1. population density, population control, population growth

2. immigration, underpopulation, urbanization

3. overpopulation, underpopulation, population limits

(the numbered choices correspond with the numbered blanks.)