If a researcher was collecting data from the same group of 30 people from infancy through childhood, they would be using the study design. a. longitudinal b. cross-sectional c. microgenetic d. experimental

a. longitudinal

Explanation:

A longitudinal study examines a given group over a long period of time, so collecting data from the same group of 30 people over their lifetime certainly fits that definition.  It's more like an evolution study.

A cross-sectional compares different groups at the same point in time.  So, it's more like a survey.

A microgenetic is much focused in time, providing multiple data sets in a short time to examine rapid evolution of a subject.

An experimental study design will make interactions and experiments with the study group, while this is not the case here apparently, and experimental is usually for a much shorter period than a generation.