Here are some simple ways to say it:
- The cat catches mice, so the farmer's grain stays safe.
- Because the cat catches mice, the farmer's food isn't eaten.
- The cat keeps mice away, which protects the farmer's grain.
Why this helps (step by step):
- The cat finds and catches the mice.
- With fewer mice, there is less eating of the grain.
- That keeps the farmer's grain safe to use.