下列有关金属腐蚀与保护的说法正确的是( ) A.常温下,断开K时,若M溶液为浓硫酸,则铁不发生化学腐蚀 B.关闭K,若M为氯化钠,则铁极的电极反应式为O2+4e-+2H2O=4OH- C.关闭K,若M为硫酸铵,则石墨极的电极反应式为2H++2e-=H2↑ D.关闭K,若M溶液为海水,石墨换成铜或银,则叫外加电流的阴极保护法一Has Lucy gone back to her home in the US?一Yes. She here only for three days with her friend.A. stayed B. will stay C. has stayed D. was staying