I followed this instruction, entering the complete code into the HTML pane of web-maker:
<!doctype html>
<html>
<head>
<title>D3 tutorial</title>
<script src="http://d3js.org/d3.v3.min.js" charset="utf-8"></script>
<!--<script src="d3.min.js"></script>-->
</head>
<body>
<script>
var canvas = d3.select("body")
.append("svg")
.attr("width", 500)
.attr("height", 500);
var circle = canvas.append("circle")
.attr("cx",250)
.attr("cy", 250)
.attr("r", 50)
.attr("fill", "red");
</script>
</body>
</html>
That results in an empty page.
The I moved the script "content" to the JS pane, that results in "ReferenceError: d3 is not defined".