Solution

The correct answer is B and C

Key PointsA. C-Fuzzy means clustering is a supervised method of learning.
            -> This statement is incorrect. Fuzzy C-means clustering is an unsupervised method, not a supervised one.

B. PCA is used for dimension reduction.
            -> This statement is correct. Principal Component Analysis (PCA) is commonly used for dimensionality reduction in machine learning.

C. Apriori is not a supervised technique.
            -> This statement is correct. Apriori is an algorithm used for association rule mining in unsupervised learning.

D. When a machine learning model becomes so specially tuned to its exact input data that it fails to generalize to other similar data, it is called underfitting.
            -> This statement is incorrect. The described scenario is an example of overfitting, not underfitting. Underfitting occurs when a model is too simple to capture the underlying                   patterns in the data.

The correct statements are B and C.