Oxygen is provided. Carbon dioxide is removed. Carbon dioxide is provided. Oxygen is removed. Carbon dioxide is provided. Nitrogen is removed. Oxygen is provided. Nitrogen is removed.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: 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?
Possibilities:
- Oxygen is provided. Carbon dioxide is removed.
- Carbon dioxide is provided. Oxygen is removed.
- Carbon dioxide is provided. Nitrogen is removed.
- Oxygen is provided. Nitrogen is removed.

Oxygen is provided. Carbon dioxide is removed.