Final answer:
The true statement is that c. pentatonic scales are often used in popular music. Pentatonic scales consist of five notes per octave and are prevalent in various genres due to their simplicity and agreeable sound, unlike the incorrect notion that they contain seven notes or are rarely used.
Step-by-step explanation:
The correct statement about pentatonic scales is that they are often used in popular music. A pentatonic scale is a musical scale with five notes per octave in contrast to the more common heptatonic scale that has seven notes. As such, it's incorrect to say that pentatonic scales are made up of seven unique notes, which rules out option A. Statements B and D are similar in claiming that pentatonic scales are not commonly used in popular music, but this is, in fact, not true. Pentatonic scales are actually quite prevalent in various genres of popular music due to their simplicity and the pleasant harmonies they generate.
Famous examples where pentatonic scales are used include songs like "My Girl" by The Temptations and "Auld Lang Syne." The simplicity of the pentatonic scale makes it a favorite for both songwriters and soloists since it's easy to create melodies that sound good over a variety of chord progressions. It's worth noting that some musicians, especially accomplished ones, may possess perfect pitch, the ability to identify or recreate musical notes without the need for a reference tone.