How Does the Body "Know" to Increase Heart and Breathing

How does the body "know" to increase heart and breathing rates when you are active?

A) Carbonic acid is produced by decreasing oxygen levels in the blood, and when the brain sensors sense the lower pH, increased rates are triggered.
B) Carbonic acid is produced when carbon dioxide dissolves in the blood, and when the brain sensors sense the lower pH, increased rates are triggered.
C) When the brain senses increased fatigue in an area of the body, it triggers increased rates.
D) The increased activity just naturally results in increased rates because the two things are correlated.
E) The hypothalamus senses low oxygen levels as blood passes through sensors there, and increased rates are triggered.