  Certain Bs --> V_1V_2 decays (V_i is a vector meson) can be related by flavor
SU(3) symmetry to corresponding Bd --> V_3V_4 decays. In this paper, we show
that the final-state polarization can be predicted in the Bs decay, assuming
polarization measurements of the Bd decay. This can be done within the scenario
of penguin annihilation (PA), which has been suggested as an explanation of the
unexpectedly large transverse polarization in B-->phi K^*. PA is used to
estimate the breaking of flavor SU(3) symmetry in pairs of decays. Two of these
for which PA makes a reasonably precise prediction of the size of SU(3)
breaking are (Bs --> phiphi, Bd --> phi K^{0*}) and (Bs --> phi {\bar K}^{0*},
Bd --> {\bar K}^{0*} K^{0*}). The polarization measurement in the Bd decay can
be used to predict the transverse polarization in the Bs decay, and will allow
a testing of PA.
