A donut chart shows the distribution of student test preparation course completion, with slices labeled by percentage. The visualization uses D3 v7's `d3.pie`, `d3.arc`, and `d3.scaleOrdinal` with the `schemeSet2` color palette, rendering in SVG. Data loads from a CSV of student performance records and is aggregated with a custom `countBy` helper. A legend displays category counts, and labels only appear for slices exceeding 6% of the total.