This stacked bar chart shows the distribution of letter grades (A, B, C, D) across five school subjects, with each bar segment representing the percentage of students receiving that grade. The visualization uses D3 v7’s `d3.stack()` to aggregate the CSV data, `scaleBand` for the subject axis, and `scaleLinear` for the percentage axis. Hovering over a segment triggers a tooltip displaying the exact percentage via mouse events. The chart is rendered as SVG with color-coded segments, using `d3.axisLeft` and `d3.axisBottom` for axes.