Longitudinal research involves Select one: a. the random selection of participants within a particular population. b. uncovering unconscious motives and conflicts. c. randomly assigning participants to the control and experimental groups. d. observing and measuring the same variables periodically over time.

The correct answer is - option D.

Explanation:

Longitudinal research involves the observational approach is gathering the data for the same variable or the subject over an extended period of time that could be years normally.

This research helps in gathering or collecting data to get insight or aspects that can not be gathered by any other way. It is used in the study or research that involves the development over the period of time such as life span.

Thus, the correct answer is - option D.

the answer is "a.) well–developed vascular system."

explanation: