A pie chart displays marks for different subjects, with each slice colored and paired with a legend identifying the subject and its numeric value. The chart reads subject and mark data from a CSV file via `d3.csv`, and uses `d3.pie` and `d3.arc` to compute the slice geometry, while `d3.scaleOrdinal` assigns categorical colors. Legends are generated as SVG groups with rectangles and text, and the whole visualization is rendered as an SVG element.