Which of the following statements describes cross-validation?
a. Cross-validation is close and intense monitoring of all the manufacturing steps and critical points in at least the first three production-scale batches.
b. Cross-validation is an automatic computer check to ensure that the data entered is sensible and reasonable and conforms to general data-type expectations. It does not check the accuracy of data.
c. Cross-validation is using historical data to provide documentary evidence that practices, policies and/or products exist in the state in accordance with their design specifications
d. Cross-validation is the process of comparing predictions of different models on a new set of data for which the actual outcomes are already known.