  $Q^2$ evolution of the structure functions $F_2$ in tin and carbon nuclei is
investigated in order to understand recent NMC measurements. $F_2$ is evolved
by using leading-order DGLAP, next-to-leading-order DGLAP, and
parton-recombination equations. NMC experimental result $\partial
[F_2^{Sn}/F_2^C]/ \partial [\ln Q^2]\ne 0$ could be essentially understood by
the difference of parton distributions in the tin and carbon nuclei. However,
we find an interesting indication that large higher-twist effects on the $Q^2$
evolution could be ruled out. Nuclear dependence of the $Q^2$ evolution could
be interesting for further detailed studies. 1. Introduction 2. Q^2 evolution
of F_2 in tin and carbon nuclei 3. Conclusions
