在理论上可用于设计原电池的化学反应是                                

A．2Al(s)十2NaOH(aq)+2H2O(1)＝2NaAlO2(ag)+3H2(g)；△H <0

B．Ba(OH)2·8H2O(s)+2NH4Cl(s)＝BaCl2(aq)+2NH3·H2O(aq)+8H2O(1)；△H >0

C．CaC2(s)+2H2O(1)→Ca(OH)2(s)+C2H2(g)；△H <0

D．FeCl3(aq)十3H2O(1) Fe(OH)3(s)+3HCl(aq)；△H >0