Final answer:
The main distinction between 1950s rock and roll and rhythm and blues is that rock and roll had a more energetic and upbeat rhythm, while rhythm and blues were smoother and more soulful.
Step-by-step explanation:
The most apparent distinction between rock and roll and rhythm and blues during the fifties is c) Rock and roll featured a more energetic and upbeat rhythm, while rhythm and blues often leaned towards smoother, soulful melodies. This difference is rooted in the origins of rock and roll, which was a combination of electric instruments with the sounds of gospel, blues, country, jazz, and R&B, creating an instant success with a heavy rhythm combined with simple lyrics and melodies that captivated teenagers. Artists like Bill Haley and Chuck Berry were at the forefront of merging these styles, and rock and roll quickly became a cultural phenomenon, influencing social interactions and challenging racial barriers.