What is the research study design in which researchers measure individuals or groups at selected ages and observe them all within a relatively short time?

Cross-sectional

Explanation:

Cross-sectional study design is an observational study design used in analyzing data gotten from a population of interest, across selected groups of people that might differ in terms of location, age, ethnicity, etc. This research study, which is also known as descriptive research, is usually conducted within the shortest time frame and are often less expensive. For example, we might use a cross-sectional study design to carry out a research on the prevalence of a certain illness in a population, of which the researcher can study people of different gender, age, location etc.

it is c and here a gift

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the answer is c.

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