Please choose the correct answer to the 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?

Answer1: Oxygen is provided. Carbon dioxide is removed. Answer2: Carbon dioxide is provided. Oxygen is removed. Answer3: Carbon dioxide is provided. Nitrogen is removed. Answer4: Oxygen is provided. Nitrogen is removed.

Answer format: answer1/answer2/answer3/answer4