题目

下述实验能达到预期目的的是 编号实验内容实验目的 A将SO2通入酸性KMnO4溶液中证明SO2的水溶液具有弱酸性 B向少量火柴头的浸泡液中滴加AgNO3、稀HNO3和NaNO2验证火柴头含有氯元素 C在淀粉－KI溶液中滴加少量市售食盐配置的溶液真假碘盐的鉴别 D在少量Fe(NO3)2试样加水溶解的溶液中，滴加稀H2SO4酸化，再滴加KSCN溶液检验Fe(NO3)2试样是否变质   ---- You ____ have finished your composition. ---- I had meant to, but before I could, the bell rang and we had to hand in our test papers. A. were supposed to   B. had to      C. were able to      D. were determined to