This visualization combines bar charts and a line chart to show average MPG and average horsepower by model year from the `mpg.csv` dataset. It uses D3 v7 APIs such as `d3.csv`, `d3.rollup`, `d3.scaleBand`, `d3.scaleLinear`, `d3.axisBottom`, and `d3.line`. The SVG rendering displays skyblue bars for mean MPG and an orange line for mean horsepower, with axes, labels, a title, and a legend.