Reductive ozonolysis of a hydrocarbon X gives methanal and the compound shown, and nothing else. Which structure is X?

The compound shown is propanedial. Two methanal molecules plus one propanedial indicate a skeleton $\mathrm{CH}{}_2=\mathrm{CH}-\mathrm{CH}{}_2-\mathrm{CH}=\mathrm{CH}{}_2$, penta-1,4-diene. Cyclohexa-1,4-diene gives only propanedial and no methanal, the conjugated diene gives ethanedial and ethanal, and hexa-1,5-diene gives butanedial.