Answer:
The answer is D. Cohort effect.
Explanation:
A cohort is a group of people that share a characteristic, in social research, such characteristic tends to be the birth year or generational designation; in these cases, cohorts might be strongly influenced by the historical and cultural environment of their generation, and this might have an effect on the results of the research project. Cross-sectional method is subject to these effects because they only apply the research techniques in one specific point in time.