  Various shadowing aspects of nuclear parton distributions are discussed in a
parton-model framework. We explain existing $x$ dependent data of
$F_2^A/F_2^D$, then the model is applied to a flavor asymmetry $\bar u-\bar d$
in a nucleus, to shadowing in valence-quark distributions, and to nuclear
dependence of $Q^2$ evolution. First, we find that a finite nuclear $\bar
u-\bar d$ distribution could be possible due to nuclear interactions even in
the flavor symmetric case in the nucleon ($\bar u -\bar d$=0). Second, it is
indicated that valence-quark shadowing could be used for discriminating among
various shadowing models. Third, we find that nuclear dependence of $Q^2$
evolution $\partial [F_2^{Sn}/F_2^C]/ \partial [\ln Q^2]$, which was found by
NMC, is essentially understood by modification of parton distributions in
nuclei. However, higher-twist effects in nuclear interactions could be tested
by studying the details of the nuclear $Q^2$ evolution.
