— What a beautiful car! When ________ you ________ it?
— I ________ it for two years.
A:did; buy; have bought
B:did; buy; have had
C:have; bought; have bought
D:have; bought; have had
下面是某实验小组的同学所做的“探究导体中电流与导体电阻的关系”的实验.
实验序号
滴加硫酸铜溶液的量
实验现象
①
第1﹣6滴
产生蓝色沉淀,但振荡后沉淀消失,形成亮蓝色溶液
②
第7﹣9滴
产生蓝色沉淀,且沉淀逐渐增多.振荡后沉淀不消失,很快沉淀逐渐变黑色