A pie chart displays the distribution of student grades from a CSV file, showing how many students received each grade. The D3 v7 code uses `d3.pie()` to compute arc angles and `d3.arc()` to generate SVG paths for each slice. Labels are positioned using a second arc generator, and a separate legend is built alongside the chart, with colors assigned via `d3.scaleOrdinal` and `d3.schemeTableau10`.