题目

下列物质属于同分异构体的一组是              A．CH4与C2H4        B．  与 CH3－CH2－CH2－CH3 C．C2H6与C3H8       D． O2与O3 答案：BDown ______ and hurt his leg.A.fell the boyB.fell heC.did he fallD.did the boy fell