Which of the following isomers of C8H18\text{C}_8\text{H}_{18}C8H18 has the lowest boiling point?
CH3(CH2)6CH3\text{CH}_3(\text{CH}_2)_6\text{CH}_3CH3(CH2)6CH3
(CH3)3C(CH2)3CH3(\text{CH}_3)_3\text{C}(\text{CH}_2)_3\text{CH}_3(CH3)3C(CH2)3CH3
(CH3)3CCH2CH(CH3)2(\text{CH}_3)_3\text{CCH}_2\text{CH}(\text{CH}_3)_2(CH3)3CCH2CH(CH3)2
CH3CH(CH3)(CH2)4CH3\text{CH}_3\text{CH}(\text{CH}_3)(\text{CH}_2)_4\text{CH}_3CH3CH(CH3)(CH2)4CH3