Line survey of Class 0 sources at the on-source position. Spectra are extracted from the central spaxel only for the well-pointed sources (for mispointed sources see text) and continuum subtracted. No correction for point spread function is made. Dashed lines show laboratory wavelengths of [O i] (pink), OH (orange), CO (red), and H₂O (blue). BHR71 and Ser SMM4 were not observed in all the lines within our program (see text).