  Internal line shifts in quasars spectra have played a more prominent role in
our understanding of quasar structure and dynamics. The observed different
redshift among broad hydrogen lines is still an amazing puzzle in the study of
quasars. We have argued that the broad hydrogen lines, as well as the
low-ionization lines in quasars, are significantly contributed by the Cerenkov
quasi-line emission of the fast electrons in the dense clouds/filaments/sheets
($N_{\rm H}\geq 10^{14}~{\rm cm^{-3}}$); whereas this line-like radiation
mechanism is invalid for producing the high ionization lines. In order to
account for redshift difference, the Cerenkov line-like radiation mechanism
could provide a plausible resolution: it is the `Cerenkov line redshift', which
is different from line to line, causes the peculiar redshift-differences among
Ly$\alpha$, H$\alpha$ and H$\beta$ lines. The different redshifts among
different broad hydrogen lines could stand for an evidence to quantitatively
support that the observed broad hydrogen lines should be blended by both the
real line emission and the Cerenkov quasi-line emission. The good fitting to
the observed redshifts of quasars confirms the existence of Cerenkov component
in the broad hydrogen lines, which indicates that, in the blended Ly$\alpha$
line, the line-intensity of the Cerenkov component approximately equals that of
the accompanying `normal line' (an approximate equipartition of intensity
between the two components in the broad Ly$\alpha$ line). This result
illustrates the importance of the Cerenkov component in the broad lines of
quasars, which can be further confirmed by future observations.
