Anna is developing a classification model. She decided to divide her dataset into 80% training and 20% testing. For the parameter tuning purpose, she used 3-fold cross validation on the training data. Which of the following is correct regarding Anna's 3-fold cross-validation process?
A. The training data is divided into four groups, models are trained on three of the groups and evaluated on the test data.
B. The training data is divided into three groups, models are trained on two of the groups and evaluated on the test data.
C. The training data is divided into three groups, models are trained on two of the groups and evaluated on the held-out group.
D. The training data is divided into four groups, models are trained on three of the groups and evaluated on the held-out group.