Which major key has 3 flats?

The major key that has 3 flats is A flat Major.

In music theory, the flat keys are constructed based on the number of flats present in their key signatures. A flat Major, specifically, is known for having three flats, which are B flat, E flat, and A flat. This is derived from the circle of fifths and can be confirmed by looking at the order in which flats are added to key signatures.

When we look at the other keys listed, E Major is a sharp key with four sharps, D flat Major has five flats, and C Major has no flats. Therefore, A flat Major stands out as the only key among the options that features exactly three flats in its key signature.