向盛有硫酸铜水溶液的试管里加入氨水,首先形成难溶物,继续添加氨水,难溶物溶解得到深蓝色的透明溶液.下列对此现象说法正确的是( )
A:反应后溶液中不存在任何沉淀,所以反应前后Cu2+的浓度不变
B:在Cu(NH3)42+离子中,Cu2+给出孤对电子,NH3提供空轨道
C:向反应后的溶液加入乙醇,溶液没有发生变化
D:沉淀溶解后,将生成深蓝色的配合离子Cu(NH3)42+
—The difficult maths problem has been solved by Tom at last.
— Indeed; and the ___ way Tom worked out the problem impressed the teacher deeply.