- Remains are parts of a dead organism
- Fossil fuels / fossils are formed from dead organisms over time
- Therefore, fossil fuels are formed from the remains of organisms

- Fossil fuels are formed from the remains of organisms
- An organism is a living thing
- Therefore, fossil fuels are formed from the remains of living things

Hence, fossil fuels are formed from the remains of living things
[Question]Fossil fuels were formed from
[Context]- Remains are parts of a dead organism 
- An organism is a living thing 
- Fossil fuels / fossils are formed from dead organisms over time