Resolving the polarization puzzles in $D^0\to VV$

We carry out a systematic analysis of the Cabbibo-favored (CF) and singly Cabbibo-suppressed (SCS) decays of $D^0\to VV$, and demonstrate that the long-distance mechanism due to the final-state interactions (FSIs) can provide a natural explanation for these mysterious polarization puzzles observed in $D^0\to VV$ in experiments. More observables, which can be measured at BESIII and possibly at LHCb, are also suggested.