Which peak would be in the mass spectrum of butanone, CH3COCH2CH3\text{CH}_3\text{COCH}_2\text{CH}_3CH3COCH2CH3, but not in the mass spectrum of butanal, CH3CH2CH2CHO\text{CH}_3\text{CH}_2\text{CH}_2\text{CHO}CH3CH2CH2CHO?
m/z=29m/z = 29m/z=29
m/z=43m/z = 43m/z=43
m/z=57m/z = 57m/z=57
m/z=72m/z = 72m/z=72
