Answer:
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.
Definitely cell phone reception! However books could be argued for since they also are a good more than a necessity. However the last 2 i believe would be classified more as necessities than goods.
~Hope this helps!~
C. Stroke if I'm not mistaken.
Good luck!
