This example demonstrates how to add and remove nodes from a force-directed graph over time. Using D3 v4, it starts with three connected nodes (A, B, C) and, after a delay, adds three new nodes, then removes and later re-adds node B with its links. The visualization relies on `d3.forceSimulation` for physics and data joins to update the SVG circles. The code uses the general update pattern with `enter()`, `merge()`, and `exit()` to handle dynamic changes, while CSS classes style nodes distinctly.