Observed spectra of CH₃OH transitions in K-band (18–26 GHz) towards W31C. The panels from (a) to (m) are arranged based on increasing frequency or increasing J for the J₂ − J₁E line series. The quantum numbers and rest frequencies of transitions are labelled in their respective panels. Class I and II CH₃OH maser transitions are labelled in red and blue, respectively, and their Gaussian fitting results are plotted in the corresponding colour. The transitions that have no maser detection yet are labelled in black, and the Gaussian fitting results are plotted in green. The vertical magenta dashed lines represent the systemic velocity of V_LSR = −3.43 km s⁻¹.