Final answer:
The correct term for estimates of future population size, age, and sex composition is population projections. These are developed using demographic data and predictions concerning birth and death rates.
Step-by-step explanation:
Estimates of future population size, age, and sex composition are called population projections. The correct answer to the student's question is a) Projections. A population projection is a prediction of future population growth or size based on assumptions about future birth and death rates. Demography, the statistical study of population changes over time, including birth rates, death rates, and life expectancies, is a key tool in creating population projections. Demographers may use life tables, which detail the life expectancy of individuals within a population, and population pyramids, which show the distribution of population by sex and age, to aid in these projections.