How does a cross-sectional study differ from a longitudinal study?

A cross-sectional study is designed to examine different subjects at a single point in time. This method allows researchers to capture a snapshot of a population, which can reveal differences and relationships among various groups. For example, it can help compare various age groups, socioeconomic statuses, or other demographics to understand how they may differ regarding specific variables like behavior or attitudes at that given moment.

In contrast, a longitudinal study involves gathering data from the same subjects repeatedly over an extended period, which enables researchers to observe changes and developments in those subjects over time. Choices focused on analyzing historical data or a single subject's in-depth analysis do not align with the primary characteristics of a cross-sectional study. Thus, the essence of option B accurately represents the fundamental difference between the two research methodologies.