把aL硫酸铵和硝酸铵的混合液分成两等份，一份加入bmol 烧碱并加热，刚好把NH₃全部赶出。另一份需消耗cmolBaCl₂,沉淀反应刚好完全，原溶液中硝酸根离子的物质的量浓度为 [ ]

A.  mol/L      

B. mol/L  

C. mol/L        

D. mol/L

If the weather had been better, we could have had a football match. Bit it ____ all day.

A．rained

B．rains

C．has rained

D．had rained