Fifteen black circles undulate in a vertical sine-wave pattern across a full-screen SVG. Each circle updates its vertical position based on a time-incremented angular offset, creating a smooth, animated wave. The example uses D3 v7's `select`, `range`, and `symbol` APIs, with a JavaScript `setInterval` driving the animation loop. Data is generated on the fly as an array of position objects, bound to circle elements via D3's data join, while SVG attributes are updated each tick.