year	averageEE
2005	0.557472
2006	0.537174
2007	0.549035
2008	0.572406
2009	0.592067
2010	0.611553
2011	0.602106
2012	0.623268
2013	0.640952
2014	0.637031
2015	0.674403
2016	0.668052

tw (kdensity averageEE ifyear==2005)(kdensity averageEE if year==2010)(kdensity averageEE ifyear==2015)(kdensity averageEE if year==2016）,legend(label(1year2005)label(2 year2010)label(3 year2015)label(4 year2016))。一直显示不对