.Suppose you have picked the parameter $\theta$ for a model using 10 -fold cross validation. The best way to pick a final model to use and estimate its error is to
A .pick any of the 10 models you built for your model; use the average CV error for the 10 models as its error estimate
B. average all of the 10 models you got; use the average CV error as its error estimate
C. average all of the 10 models you got; use the error the combined model gives on the full training set
D. train a new model on the full data set, using the $\theta$ you found; use the average CV error as its error estimate
