One characteristic of the song that would most accurately represent the music of this period is this: d), "It has a wide range of notes and chords"
What is the characteristic?
The reason for the above response is that Romanticists favored emotional expression and individuality, often using complex melodies and harmonies to convey these emotions.
This meant they were not afraid to explore a wide range of notes and chords, often venturing beyond the traditional harmonic structures of the Classical period.
For this reason, focusing on the wide range of notes and chords in the song would be the most accurate way for Catherine to determine if it belongs to the Romantic period.