Aresearcher is studying how depression tends to be experienced by people of different ages. the researcher interviews depressed adolescents, young adults, individuals in their 30s and 50s, and those over 70 years old. the research design being used is called

The research design being used is called cross-sectional study.

Explanation:

Cross-sectional studies aime to study the behavior of a variable within a population at a specific point in time. This design can also be used to study the same variable within different subsets of a population, these subsets can be different age cohorts, different gender or race. The distinct characteristic is that the study takes place at one specific point in time, and not throughout several years, like a longitudinal study would be.

In this case, the researcher categorized the population by age cohorts and aimes to study depression amongst these different groups at a specific point in time.

marginal cost is a microeconomic measure that us to evaluate the extent to which the level of production of a good is sustainable in accounting, that is, to how many quantities the company plans to profit from the production of the good.

the concept of marginal cost is simple, it means the cost of producing one more item. for example, in the case of pies, the marginal cost is the cost of producing one more pie than those that have already been produced.

it is important to understand that productive activity influences marginal cost. the marginal cost of some goods can be very high, while others may be insignificant. for example, the marginal cost of producing an extra plane is very high. already the marginal cost of a water company to provide 1l more water is derisory.

in the case of pies, the cost involves the inputs, the labor and the fixed cost, which involves the fixed space of the bakery. the level of production initially has the marginal cost decreasing because there is space and manpower available. however, to produce more you have to hire more workers and buy more inputs. if physical space is limited, workers will conflict with places, inputs and their productivity will decrease, meaning there is an optimum point of production for each level of space and manpower. from this point on, the productivity of the workers will be getting smaller because of lack of space, so that the marginal cost of producing one more pie will be increasing. so, although you have not posted the chart, but if you have the answer, you can see that my explanation goes according to the marginal cost curve that will increase from the 4th pie, answer (c).