A pie chart visualizes the total exam score contribution for each grade category (A–D) using data from a 120-row CSV file. The D3.js v7 code loads the data, aggregates scores by category with `d3.rollup` and `d3.sum`, and renders slices via the `d3.pie` and `d3.arc` generators. Interactive tooltips appear on hover, displaying each category's total and letter label. A legend maps colors from `d3.scaleOrdinal` with the Tableau10 scheme, and the SVG output is white-stroked.