Concept:Cleaning and greasing metal parts after use helps to protect them from rust and moisture damage.
Explanation:After use, plough discs often have soil, water, and plant sap on them.
If they are left dirty and wet, the metal reacts with moisture and oxygen in the air.
This reaction causes rust to form on the iron or steel discs, weakening them.
Greasing the discs creates a thin protective layer that blocks moisture from touching the metal surface.
Therefore, cleaning off dirt and applying grease is mainly done to keep the discs from rusting.
Answer:A. prevent rusting