This visualization displays health expenditure trends in the US, showing multiple lines for different age groups over time. It uses D3.js v5 with SVG rendering and animated transitions to draw the line chart. A dropdown menu allows users to select different expenditure columns, triggering a smooth 1.5-second transition animation that redraws the lines. The chart includes a color legend for age categories and uses D3's `scaleTime`, `scaleOrdinal`, `nest()`, and `line()` APIs.