Please answer the following question: Answer the following question given this paragraph: Aerobic respiration , which takes place in the presence of oxygen, evolved after oxygen was added to Earth's atmosphere. This type of respiration is useful today because the atmosphere is now 21% oxygen. However, some anaerobic organisms that evolved before the atmosphere contained oxygen have survived to the present. Therefore, anaerobic respiration , which takes place without oxygen, must also have advantages. Q: Anaerobic respiration takes place without what? Choices: - nitrogen - movement - carbon - oxygen A:
A:
oxygen