Which compound can be dehydrated to form an alkene?
CH3COCH3\text{CH}_3\text{COCH}_3CH3COCH3
CH3CH2CH2OH\text{CH}_3\text{CH}_2\text{CH}_2\text{OH}CH3CH2CH2OH
CH3CH2CHO\text{CH}_3\text{CH}_2\text{CHO}CH3CH2CHO
CH3CH2COOH\text{CH}_3\text{CH}_2\text{COOH}CH3CH2COOH