_________ should not be allowed to go out at night. A. Twelve-years-old B. Twelve-year-olds C. Twelve year old D. Twelve years olds 答案:B6.有下列物质:①11H与21H;②O2与O3;③CH3CH2CH2CH3与;④CH4与C3H8;⑤CH3CH2CH2CH3与 .请回答下列问题:(1)互为同位素的是①(填序号,下同).(2)互为同系物的是④.(3)互为同分异构体的是③.(4)属于同一种物质的是⑤.(5)用系统命名法命名的名称是2-甲基丙烷.