What musical scale, a seven-tone equidistant system, underpins Thai classical music?

• A Equal-tempered heptatonic ✓
• B Pentatonic scale
• C Diatonic scale
• D Chromatic scale

Thai classical music uses a theoretically equidistant seven-tone scale (equidistant heptatonic) where the octave is divided into seven roughly equal steps, distinct from Western tuning.