Which alkene gives propanone as the only organic product on reductive ozonolysis?

$(\mathrm{CH}{}_3){}_2\mathrm{C}=\mathrm{C}(\mathrm{CH}{}_3){}_2$ is symmetrical and both ends become $(\mathrm{CH}{}_3){}_2\mathrm{C}=\mathrm{O}$. 2-Methylpent-2-ene gives propanone and propanal, 2-methylbut-2-ene gives propanone and ethanal, and 2-methylpropene gives propanone and methanal.