- Photosynthesis means green plants convert from carbon dioxide and water and solar energy into carbohydrates and food and oxygen for themselves
- If a process converts something to something else, then that something has the role of raw material in that process
- So, in the photosynthesis process carbon dioxide has the role of raw material

- Photosynthesis is a kind of chemical process
- If something is a raw material in a process then that something is required for that process
- So, if something is a raw material in photosynthesis then that something is required for photosynthesis

- In the photosynthesis process carbon dioxide has the role of raw material
- If something is a raw material in photosynthesis then that something is required for photosynthesis
- So, carbon dioxide is required for photosynthesis

- If something is required for a process then that something is used in that process
- Photosynthesis is a kind of chemical process
- Hence, if something is required for photosynthesis then that something is used in photosynthesis

- Carbon dioxide is required for photosynthesis
- If something is required for photosynthesis then that something is used in photosynthesis
- Therefore, carbon dioxide is used in photosynthesis

Hence, carbon dioxide is used in photosynthesis
[Question]Which of the following gases do plants use in photosynthesis?
[Context]- Photosynthesis means green plants convert from carbon dioxide and water and solar energy into carbohydrates and food and oxygen for themselves 
- If something is required for a process then that something is used in that process 
- If a process converts something to something else, then that something has the role of raw material in that process 
- Photosynthesis is a kind of chemical process 
- If something is a raw material in a process then that something is required for that process