The extracted [C II] spectra of the two quasars (step plots) and the best-fit Gaussian profile for the lines (solid lines). The two quasars have [C II] redshifts of z_{[C II]} = 5.69 and do not show a significant line-of-sight velocity difference. We note that the [C II] lines fall on the edge of the spectral windows, and the continuum with frequency lower than 283.50 GHz is not covered.