In Humans, the Body Needs to Maintain Oxygen Levels Within

In humans, the body needs to maintain oxygen levels within narrow homeostatic ranges. If the blood oxygen level drops below that range, the body responds by

A) using positive feedback to further lower the oxygen level.
B) using negative feedback loops to further lower the oxygen level.
C) setting this lower oxygen level as the new normal.
D) using negative feedback loops to return the oxygen level to normal.
E) using positive feedback to raise the oxygen level.