The correct answer is D – F1 score, which is the harmonic mean of precision and recall. AWS documentation states that the F1 score is the preferred metric when evaluating ML models trained on imbalanced datasets, where one class appears significantly more often than others. Accuracy becomes misleading in these situations because a model can achieve high accuracy simply by predicting the majority class. Precision alone measures correctness of positive predictions, while recall measures completeness—neither fully captures class balancing performance. The F1 score provides a combined measurement that reflects how well the model identifies minority classes while avoiding excessive false positives. AWS’s ML Specialty Guide recommends using F1 for classification tasks where “class distribution is uneven or where both false negatives and false positives matter.” This metric provides a fairer assessment of overall model performance across all class categories.

Referenced AWS Documentation:

AWS Certified Machine Learning Specialty Guide – Metrics for Imbalanced Classes

Amazon SageMaker Developer Guide – Evaluating Classification Models