Let's make a face with D3.js!
A smiling face is drawn with SVG shapes, with its eyebrows animating up and down in a repeating loop. The example demonstrates fundamental DOM manipulation in D3.js v5, using `select` and `append` to build circles, rectangles, and a path. The mouth is created with the `d3.arc` API, and the eyebrow motion relies on chained `transition().duration()` calls to alternate the transform attribute, creating a simple, continuous facial animation.