Answer
There will be one other ressonance structure.
It will follow the first pattern, a lone pair next to a pi bond.
The electrons from the pi bond will move to the oxygen above them, and a lone pair from the other oxygen will form a pi bond with the left carbon.
Work Step by Step
1. Draw the lone pairs.
2. Find which pattern does that structure fits.
It is the first one, a lone pair (from the oxygen that doesn't have pi bonds) next to a pi bond.
3. Draw the arrows:
Follow the pattern for a lone pair next to a pi bond.
The electrons from the pi bond will move to the oxygen above they, so the carbon that lost the pi bond will get a positive charge.
Then, the lone pairs from the other oxygen will form a pi bond with this positive carbon.
4. Do the changes based on the arrows.
* Don't forget the formal charges!
