Explanation

(a)
During rusting, oxidation of iron takes place, $i.e.\$, it acts as anode. Hence, coating/connecting iron with metal of lower reduction potential (in comparison to iron) is the best way to prevent its rusting. In this process, the metal with low reduction potential undergoes oxidation ($i.e.$ acts as anode) while iron acts as cathode. (Cathodic protection)
Use of saline water accelerates the process of rusting thereby increasing the electric conduction of electrolyte solution formed on the metal surface.