Which option is an example of unsupervised learning?

Unsupervised learning involves training a model on unlabeled data, letting it find patterns or groupings on its own, without explicit outputs provided. Clustering is a primary unsupervised learning technique.

Option A is correct: Grouping customers based on purchase history (without predefined categories) is clustering, a classic unsupervised task.

B and C are supervised learning (classification and regression, respectively).

D is reinforcement learning, not unsupervised learning.

"Unsupervised learning involves training on data without labels and is often used for clustering or dimensionality reduction."

(Reference: AWS Certified AI Practitioner Official Study Guide, AWS ML Concepts)