$(1\mathrm{.}5$ marks$)$ What are the three types of wear?

$(1$ mark$)$ Galvanic corrosion is a process when two $($or more$)$ metals interact with each other in a corrosive environment $($electrolytic solution$).$ Shown in the figure is how the process works from a chemist's point of view. Of the two metals shown, which one is corroding?

$(3$ marks$)$ What are some of the key preventative maintenance activities for lubricated systems?