Library in addition to d3 needed, projection not needed

What is your hint or solution suggestion?
– in order to parse the data from which the map is to be drawn, we need another library, whose identity will probably show up if you poke around on Google or check out the example.

–There is no need to define a projection for this county data! When I researched how to draw maps from the kind of file we were given, everything I found said to define a projection (geoAlbers, geoMercator, e.g.). I did this and got the some of the most beautiful digital abstract art I’d ever seen instead of a map; turns out this data has already been adjusted to use a projection, so when I skipped that step (as I saw to do from the example page) I got a map!

Challenge: Visualize Data with a Choropleth Map

Link to the challenge: