This example visualizes the average reading score by age as a line chart, highlighting trends in performance across different age groups. It uses D3.js (v7) to fetch a CSV dataset, group the data by age, and compute the mean reading score for each age. The chart is rendered as an SVG element, with scales mapping age to the x-axis and average reading score to the y-axis. A green line path, generated via `d3.line`, connects the data points, while axes are added using `d3.axisBottom` and `d3.axisLeft` with labels for clarity.