More than 20 people ________ in traffic accidents ________ last May.

A．have died, for

B．have died, since

C．have been dead, since

D．have been dead, for

下列实验方案不能达到目的是（　　）

A．用磁铁除去铜粉中混有的少量铁粉

B．用天然水制蒸馏水时加几粒碎瓷片，防止暴沸

C．将熟石灰与某固体混合研磨并闻气味，检验该固体中是否含有NH₄⁺

D．用银、硫酸亚铁溶液、氯化铜溶液探究银、铁、铜三种金属的活动性顺序