Can you think of some cases___________students know clearly he should listen to the teacher but can’t do that ?

A．where

B．as

C．why

D．which

下列化学方程式正确的是（　　）

A．AgCl+HNO₃═AgNO₃+HCl

B．ZnCO₃+CaCl₂=CaCO₃↓+ZnCl₂

C．Na₂CO₃+2KNO₃═K₂CO₃+2NaNO₃

D．Zn+CuCl₂═ZnCl₂+Cu