题目

下列反应中原子利用率没有达到100%的是 A制取乙醇:CH2=CH2+H2OCH3CH2OH B.制取环氧乙烷：2CH2=CH2+O22 C.制取氯乙烯：4CH2=CH2+O2+2Cl24CH2=CHCl+2H2O D.制取环已烷: +3H2 答案：CThey have been away from here since two years ago．（改为同义句）________ ________two years________they left here．