  High-energy spin physics became a popular topic recently after the EMC
finding for the proton's spin content. There exist unmeasured spin-dependent
structure functions ($b_1$, $b_2$, $b_3$, and $b_4$) for spin-one hadrons such
as the deuteron. The tensor structure function $b_1(x)$ could be measured by
the proposed 15 GeV European Electron Facility. The measurement provides
important clues to physics of non-nucleonic components in spin-one nuclei and
to tensor structures on the quark-parton level.
