  Recently, it was pointed out that the solar and atmospheric neutrino deficits
can be explained by oscillations between electroweak doublet and singlet
neutrinos in the model of Majorana neutrinos. However, since the model includes
no flavor mixing, it cannot explain the recent LSND result. We extend the model
to include the flavor mixing, and obtain the explanation of the LSND result
together with the solar and atmospheric neutrino deficits. The requirement for
the neutrinos to be the hot dark matter selects out only the vacuum oscillation
solution to the solar neutrino deficit.
