Regression results of = () + are given in the left plot below, where black curve is truth. Red curve on right plot is test error, and grey curve is training error. Which model among yellow, blue, and green is the best? and why? (explain in terms of test error and training error)

Y 2 9 8 10 12 0 20 40 60 80 100 Mean Squared Error 0.0 0.5 1.0 1.5 2.0 2.5 2 5 Flexibility 10 20 Y 2 9 8 10 12 0 20 40 60 80 100 Mean Squared Error 0.0 0.5 1.0 1.5 2.0 2.5 2 5 Flexibility 10 20