About _________ of the engineers in my company seem to be in their _________.
A:second-nines; forties
B:two-ninths; forties
C:second-ninths; fortieth
D:two-ninths; fortieth
某化学兴趣小组,为验证Ag、Fe、Cu三种金属的活动性顺序,设计了如图所示的实验操作,其中可以达到实验目的组合是( )
仿写
绿茵茵 ____ ____ ____