在Ba（NO₃）₂、AgNO₃、Cu（NO₃）₂溶液中分别滴入一种试剂都有沉淀产生．该试剂可能是（　　）

A．盐酸

B．硫酸

C．Na₂CO₃溶液

D．NaOH溶液

There is a blackboard ______ our classroom. [ ]

A. in front of

B. in front off

C. in the front of

D. the front of