The final examination of this term is coming, so every one of us ________ for it these days[ ]

A．has prepared  

B．prepared

C．has been preparing  

D．was preparing

下列的腐蚀中哪些属于局部腐蚀？（）

A.电偶腐蚀

B.金属的高温氧化

C.金属表面大面积锈蚀。

D.钢构件表面失泽发暗。