Concept:The cross-sectional approach studies development by comparing different age groups at a single point in time.
Explanation:An approach is a viewpoint that includes specific assumptions about human behaviour and the research methods best suited to study it.
A cross-sectional study gathers data from many different individuals at one specific point in time.
In this approach, representative samples of different age groups, such as one-year-olds, two-year-olds, and three-year-olds, are assessed simultaneously.
Since the performance of various age groups is compared at the same time rather than tracking the same individuals over time, this is a cross-sectional approach.
A longitudinal study, in contrast, requires repeated observation of the same participants over an extended period to detect changes.
The longitudinal approach repeatedly observes the same group and tracks participants' changes over time.
As the question involves comparing different age groups at a single time, it clearly indicates the cross-sectional approach.
Answer:B. Cross-sectional Approach