在H₂S+2OH^-=S^2-+2H₂O的离子反应中，OH^-所代表的是（硫化铜难溶于水）（  ）

A．KOH

B．Cu(OH)₂

C．Mg(OH)₂

D．NH₃·H₂O

So sudden ________that the enemy had no time to escape. 

A．did the attack

B．the attack did

C．was the attack

D．the attack was