Answer the following question given this paragraph: 

Keeping the rate of metabolism high takes a constant and plentiful supply of oxygen. That’s because cellular respiration, which produces energy, requires oxygen. The lungs and heart of mammals are adapted to meet their oxygen needs.


Q: A constant and plentiful supply of oxygen is required in order to maintain a high rate of what?

 Choices:

- digestion

- cell division

- magnesium

- metabolism

A:
metabolism
