- Breathing is a process in animal respiration
- Animals require respiration to survive / use energy
- Hence, animals must breath to survive

- Animals must breath to survive
- Breathing is when animals convert oxygen into carbon dioxide
- Hence, an animal requires oxygen for survival / to breathe

- An animal requires oxygen for survival / to breathe
- If something is required by something else then that something must be provided to that somethign else
- Hence, oxygen must be provided to animals in order for them to breathe / survive

- Some environments contain waste
- Waste must be removed
- Therefore, waste must be removed from environments that contain waste

- Breathing out is when animals expel carbon dioxide from their lungs into the air
- If something is expelled in a process, then that something is a waste product of that process
- So, carbon dioxide is a waste product of the breathing process

- Carbon dioxide is a waste product of the breathing process
- Breathing is a process in animal respiration
- Therefore, in the animal respiration process carbon dioxide is a waste product

- Waste must be removed from environments that contain waste
- In the animal respiration process carbon dioxide is a waste product
- So, carbon dioxide must be removed from an environment where animals are performing respiration

- Oxygen must be provided to animals in order for them to breathe / survive
- Carbon dioxide must be removed from an environment where animals are performing respiration
- Hence, in an environment where animals are breathing / performing respiration, oxygen must be provided and carbon dioxide must be removed

Therefore, in an environment where animals are breathing / performing respiration, oxygen must be provided and carbon dioxide must be removed
Q: As humans travel in space, which gas is provided in the atmosphere of the spacecraft and which gas is removed from the atmosphere of the spacecraft?
Context:
- Breathing is when animals convert oxygen into carbon dioxide 
- If something is required by something else then that something must be provided to that somethign else 
- Breathing is a process in animal respiration 
- Some environments contain waste 
- Breathing out is when animals expel carbon dioxide from their lungs into the air 
- If something is expelled in a process, then that something is a waste product of that process 
- Waste must be removed 
- Animals require respiration to survive / use energy