  The recent progress in studies of two-nucleon~(2N) short-range
correlations~(SRCs) are reviewed with the main emphasize given to the
observation of the strong dominance of proton-neutron~(pn) SRCs in nuclei as
compared to proton-proton and neutron-neutron SRCs. Based on the pn SRC
dominance a specific prediction is made for the dynamical structure of 3N- SRCs
for inclusive $A(e,e^\prime)X$ reactions, according to which the 3N- SRCs are
generated through the sequence of two short range $pn$ interactions. This
allowed us to predict that the height of the plateau in the ratios of inclusive
eA cross sections to that of $^3He$ in the 3N-SRC region is related to the
height of the plateau in the 2N-SRC region by a quadratic relation. The
analysis of the available experimental data supports validity of such a
relation.
