题目

某化学兴趣小组对奥运会金牌成分提出猜想：甲认为金牌是由纯金制成；乙认为金牌是由金银合金制成；丙认为金牌是由黄铜(铜锌合金)制成。为了验证他们的猜想，请你选择一种试剂来证明甲、乙、丙猜想的正误  ( )。 A．硫酸铜溶液                         B．稀硝酸 C．盐酸                               D．硝酸银溶液I could sense that tile manager wasn't satisfied with our work ________ he didn't say anything．A.ifB.unlessC.althoughD.when