题目

下列物质在给定条件下的转化均能一步实现的是（） A . Fe3O4 Fe FeCl3 B . H2O2 H2 H2O C . CaCl2溶液 CaCO3 CO2 D . CuSO4溶液 Cu CuO 答案：DEighteen kids died in the school bus accident in Gansu Province. It's _____ one that I have everheard of.      [     ]A. a very serious     B. a more serious    C. the most serious     D. the least serious