New tests of quark-parton model

It is shown that a simple constraint between $\frac{F_2^{\mu n}}{F_2^{\mu p}}$ and $\frac{F_2^{\nu p}}{F_2^{\mu p}}$ derived from the basic properties of QCD that are contained in the quark-parton model is not satisfied by the present experimental data. The measurement of semi-inclusive cross sections that may clarify the issue on the $\frac{d}{u}$ ratio is suggested.