题目

                                                             已知反应X+3O22CO2+2H2O，则X的化学式为（ ）                A．C2H6              B．C2H4              C．C2H2              D．C2H6O 答案：【考点】质量守恒定律及其应用．                                  【专题】化学用语和质量守恒定律．                                【分析】根据反应X+3O22CO2+2H2O，利用质量守恒定律的元素守恒来推断X的化学式．          【解答】解：                 阅读下列短文，从每题所给的四个选项(A、B、C、D)中选出最佳选项。 　　Bob is American．He is forty-one．His wife, Kate is thirty-eight．She is a good wife and a good mother．They love their four children．Two of them are daughters．Their names are Mary and Linda．They are twins．Jim and Sam are their sons．Their young son, Sam, is fifteen．Jim is eighteen now．He loves his family．They have two cats．They are both three．Their names are Mimi and Lili． (1) How many people are there in Bob's family? [　　] A． Four B． Five C． Six D． seven (2) Who is Mary? She is ________． [　　] A． Kate's sister B． Jim's sister C． Sam's mother D． Linda's mother (3) How old are their cats? [　　] A． one B． two C． three D． four