Which peak would be observed in the mass spectrum of pentan-3-one, CH3CH2COCH2CH3\text{CH}_3\text{CH}_2\text{COCH}_2\text{CH}_3CH3CH2COCH2CH3, but not in the mass spectrum of pentan-2-one, CH3COCH2CH2CH3\text{CH}_3\text{COCH}_2\text{CH}_2\text{CH}_3CH3COCH2CH2CH3?
m/z=43m/z = 43m/z=43
m/z=57m/z = 57m/z=57
m/z=71m/z = 71m/z=71
m/z=86m/z = 86m/z=86