  First observations of the B_s0->D_s*- pi+, B_s0->D_s- rho+ and B_s0->D_s*-
rho+ decays are reported together with measurements of their branching
fractions: B(B_s0->D_s*- pi+)=(2.4 +0.5-0.4(stat.) +-0.3(syst.)
+-0.4(fs))x10^(-3), B(Bs->D_s- rho+)=(8.5 +1.3-1.2(stat.) +-1.1(syst.)
+-1.3(fs))x10^(-3) and B(Bs->D_s*- rho+)=(11.8 +2.2-2.0(stat.) +-1.7(syst.)
+-1.8(fs))x10^(-3) (f_s=N(B_s(*)B_s(*)-bar)/N(b b-bar)). From helicity-angle
distributions, we measured the longitudinal polarization fraction in
B_s0->D_s*- rho+ decays to be f_L(Bs->D_s*- rho+)=1.05 +0.08-0.10(stat.)
+0.03-0.04(syst.). These results are based on a 23.6 /fb data sample collected
at the Y(5S) resonance with the Belle detector at the KEKB e+e- collider.
