What is a key signature with no sharps or flats?

A key signature with no sharps or flats corresponds to both C major and its relative minor, A minor. In Western music, C major is the major scale that starts on the note C and consists of the pitches C, D, E, F, G, A, and B. Since it contains no accidentals (sharps or flats), it is represented with a key signature that has nothing on the staff.

A minor, which is the natural minor scale relative to C major, also has a key signature with no sharps or flats. This is significant, as both keys share the same tonal characteristics and come from the same set of pitch classes.

The other options listed, E major and D minor, have key signatures that include sharps or flats. E major, for instance, has four sharps, while D minor typically has one flat in its natural form. Understanding the relationship between major and minor scales and their key signatures is crucial in music theory, particularly when identifying the effective key of a piece based on its signature.