Creating a circle is very easy, and we’ve already touched on it before when making Points.
myCircle = drawing.append("circle")
.style("stroke", "Black") // Outline with Black
.style("fill", "none") // Do not fill
.attr("r", 100) // Draw it with a radius of 100
.attr("cx", 100) //x of the centre or "centreX"
.attr("cy", 100) //y of the centre or "centreY"