This chart displays the frequency of letters A through G as a bar graph, with each bar color-coded and clickable to highlight a selected letter. Built with React and D3 v7, it loads data from a CSV file using `d3.csv`, scales the bars with `d3.scaleBand` and `d3.scaleLinear`, and renders axes via `d3.axisBottom` and `d3.axisLeft` with gridlines. A `ResizeObserver` in React tracks container dimensions for responsive redrawing, while D3 transitions animate bar color and opacity on selection.