Early Beatles songs demonstrate harmony and form through the following: A. Predominantly following the verse-refrain-chorus-bridge structure, albeit with variations. B. Major key songs influenced by Buddy Holly, using primarily I, IV, and V chords. C. Twelve-bar blues compositions employing the I-IV-V chord progression. D.All of the choices

D. All of the choices

The early songs by The Beatles demonstrate their mastery of harmony and song structure through all of the listed mechanisms:

A. Verse-refrain-chorus-bridge structure: Early Beatles songs often followed this common structure, providing a clear and familiar framework for listeners. While they adhered to this structure, they also introduced variations to keep their songs fresh and engaging.

B. Major key songs influenced by Buddy Holly using primarily I, IV, and V chords: The Beatles were influenced by early rock 'n' roll artists like Buddy Holly, and this influence is reflected in their use of major keys and simple chord progressions that overwhelmingly use the tonic (I), subdominant (IV), and dominant (V) chords. These chords create a solid, pleasant harmony that was easily digested by the pop audiences of the time.

C. Twelve-bar blues compositions employing I-IV-V chord progression: Some of The Beatles' early works also drew from the blues genre, as evidenced by their use of the twelve-bar blues form, a staple in blues music. This form also revolves around the I, IV, and V chords and follows a specific pattern that repeats throughout the song, providing a familiar structure for improvisation and variation.