题目

Peter’s uncle lives in the country. He is a man full of humor (幽默). One day， Peter went to see his uncle. His uncle drove his car to the station to meet him. On their way home， they saw many people. His uncle waved (挥手) to everybody. Peter was surprised (惊奇) and said，“Uncle，you wave to everybody. Do you know all of them?” “No，Peter，” answered his uncle. “When I wave to someone who knows me， he’ll feel happy. When I wave to someone and he doesn’t know me， he will feel surprised and then he will have something to think about，he will make his r一种气态烷烃和一种气态烯烃组成的混合气体共10g，其密度是相同条件下H2的12.5倍，该混合气通过Br2水时，Br2水增重8.4g，则组成该混合气的可能是（　　）A．甲烷、乙烯B．丙烷、乙烯C．乙烷、丙烯D．甲烷、丙烯