Which of the following can undergo dehydration with dilute $\mathrm{NaOH}$ by the E1cB mechanism?

E1cB dehydration requires an alpha-hydrogen on the carbon between C=O and the beta-carbon that bears the OH. 3-Hydroxybutanal, 4-hydroxy-4-methylpentan-2-one and 3-hydroxycyclohexanone all have such an alpha-H (the last gives cyclohex-2-enone). In $\mathrm{HOCH}{}_2-\mathrm{C}(\mathrm{CH}{}_3){}_2-\mathrm{CHO}$ the alpha-carbon is quaternary and has no hydrogen, so no enolate can form.