Final answer:
When Christmas music is performed in another country's style, it's the instrumentation and arrangement that may vary, infusing the piece with local musical traditions while generally keeping the melody recognizable.
Step-by-step explanation:
When a piece of Christmas music is performed in another country's style, the main difference you typically encounter is C) The instrumentation and arrangement may vary. The fundamental melody of the song often remains the same to maintain its recognizable tune. However, the instruments used and the way the song is arranged can change to reflect regional musical traditions. For instance, a Christmas song played in a Latin American style might feature guitars, maracas, and trumpets, producing a sound that's distinct from the original.