向一无色透明的溶液中滴加稀硫酸时有沉淀生成，且所得沉淀量与所加硫酸的关系如下图所示，则原溶液可能是 

A．Na₂SiO₃与Na₂CO₃的混合溶液

B．Na₂S和Na₂SO₃的混合溶液

C．NaAlO₂与Na₂SiO₃的混合溶液

D．Na₂SO₃与Na₂SiO₃的混合溶液

_________ trees have been planted these years.

A．Million

B．Millions

C．Million of

D．Millions of