As we know, the Changjiang River is one of _______rivers in the world.

A. long                                   B. longer                                       C. the longest

现有锌片、铝片和铜片，某兴趣小组为研究它们的活动顺序，需要的试剂是（　　）

A．氯化银

B．稀盐酸

C．氯化铝溶液

D．硫酸钠溶液