- Pilot, Driver, Gardener: Engage in service-based activities (tertiary sector).
- Fisherman, Teacher, Lawyer: Belong to different economic sectors, but majorly service-oriented.
- Doctor, Teacher, Lawyer: Belong to the tertiary sector (service industry).
- Engineer, Professor, Farmer: Farmer belongs to the primary sector (agriculture), making this group inconsistent.
Conclusion: The odd one out is \( \mathbf{(C)} \) because the farmer is from the primary sector while the others belong to different sectors.