When I talked with my grandma on the phone, she sounded weak, but by the time we ________ up, her

voice had been full of life.[ ]

A．were hanging 

B．had hung

C．hung  

D．would hang

钢铁生锈现象随处可见，钢铁的电化学腐蚀原理如图所示：

(1)写出石墨电极的电极反应式_____________________.

(2)将该装置作简单修改即可成为钢铁电化学防护的装置，请在图中虚线框内所示位置作出修改，并用箭头标出导线中电子流动的方向．

(3)写出修改后石墨电极的电极反应式_________________________________________．