The problem of finding hidden structure in unlabeled data is called . . . . . . . .

The correct answer is B. unsupervised learning.

Unsupervised learning is a type of machine learning in which the computer is not given any labeled data. Instead, the computer is given a set of data and must find patterns in the data on its own. This type of learning is often used for tasks such as clustering and dimensionality reduction.

Supervised learning is a type of machine learning in which the computer is given a set of labeled data. The labels tell the computer what the correct output should be for each input. The computer then learns to map inputs to outputs. This type of learning is often used for tasks such as classification and regression.

Reinforcement learning is a type of machine learning in which the computer learns to take actions in an environment in order to maximize a reward. The computer is not