http://digfir-published.macmillanusa.com/gls_animated_graph/gls_2_9.html\tChapter 1. eFigure 2.9 \t515f2aeeb11c0ffa13000001 http://digfir-published.macmillanusa.com/gls_animated_graph/gls_2_9_dlap.xml\tDLAP questions\t515f2aeeb11c0ffa13000001