You are creating a retraining policy for a customer churn prediction model deployed in Vertex AI. New training data is added weekly. You want to implement a model retraining process that minimizes cost and effort. What should you do?

A. Retrain the model when a significant shift in the distribution of customer attributes is detected in the production data compared to the training data. B. Retrain the model when the model's latency increases by 10% due to increased traffic. C. Retrain the model when the model accuracy drops by 10% on the new training dataset. D. Retrain the model every week when new training data is available.