What is the difference between nr and r rated?

i started to read this expecting to actually answer something serious but i was wrong that was the first time i laughed today

explanation:

changeable lenses of different focal lengths allow light to enter the camera, which then forms the image on light-sensitive film" is the one among the following statements about working principle behind a basic still camera is true.

a chromatic scale uses the twelve tones of the octave, while a regular scale only uses eight, or seven different notes (as the first note is played twice)