Which compounds in problem are isomers? a)2-methylpropane b)2,4-dimethylpentane c)2,2-dimethylpentane d)4-ethyl-2-methylhexane e)2,3-dichloro-4-t-butylheptane f)4-ethyl-7-isopropyl-2,4,8-trimethyldecane g)4-isobutyl-3,4-dimethyl-5-sec-butyloctane h)1,2-dimethylcyclohexane i)methylcyclopropane