Measured spectral lines: 500.5, 557.7, 568, 575.5, 630, 636.4, 648.2, 655.3 nm. Laboratory reference lines: Nitrogen + Argon: 415.9, 420.1, 500.5, 568, 575.5, 648.2, 655.3, 696.5, 706.7 nm; Hydrogen + Nitrogen: 410.2, 434, 486.1, 500.5, 568, 575.5, 648.2, 655.3, 656.3 nm; Nitrogen + Carbon: 426.7, 477.2, 493.2, 500.5, 568, 575.5, 648.2, 655.3, 658 nm; Oxygen + Nitrogen: 500.5, 557.7, 568, 575.5, 630, 636.4, 648.2, 655.3 nm. Which element mixture best accounts for all of the observed lines?