Exercise : add 8 more cubes and set their color to blue. http://jsbin.com/civivo/edit?html,output
Exercise 2, more complicated : add a number of cubes that change every time you reload the page. http://jsbin.com/civivo/edit?html,output
Exercise 3, even more complicated : add an increasing number of different primitive, e.g. 3 cubes, 4 spheres, 5 torus, etc. http://jsbin.com/civivo/edit?html,output