What is the correct structure for sulfur dioxide? A question from the National Chemistry Olympiad (Germany-2008) goes as follows:


  Besides the composition of a substance the structure of its molecule or ion is of interest. To predict the structure you may use the electron repulsion theory
  (VSEPR).
  The following sulphur compounds are choosen as examples
  $\ce{SO2}$, $\ce{SO3(g)}$, $\ce{SOF2}$, $\ce{SO4^2-}$, $\ce{SF4}$, $\ce{SOF4}$, $\ce{SF6}$.
  
  b) Draw the structure of these species. Insert the free electron pairs of $\ce{S}$.
  Give the name of the geometrical shape of these compounds or ions.


I'm only interested in the structure of $\ce{SO2}$, that is represented in the answer sheet as $\ce{O=S-O}$ instead of the one I believe is the correct one $\ce{O=S=O}$.

What do you think?
See this.
It's because it can be thought as two interchangeable resonant structures. What happens in reality is that the electron is delocalized over the three atoms.