Class imbalance occurs when one class significantly outnumbers another, causing models to bias predictions toward the majority class. In this case, images without defects (1,800) vastly outnumber images with defects (200). AWS ML best practices recommend oversampling the minority class to improve class representation without discarding valuable data.

Oversampling techniques—such as duplicating minority samples or applying data augmentation—help the model better learn defect-related features. This approach preserves all available data and improves recall and precision for underrepresented defect classes.

Option B is incorrect because undersampling the minority class would further worsen imbalance. Option A unnecessarily reduces dataset size. Option D does not address the imbalance problem.

Thus, oversampling defect images is the correct solution.