Although Children Believe That "Holding My Breath Until I Die

Although children believe that "holding my breath until I die" is possible, parents know this to not be true because

A) as a child holds his or her breath, oxygen levels build, stimulating breathing by the brain stem.
B) as a child holds his or her breath, oxygen levels decrease, stimulating breathing by the brain stem.
C) as a child holds his or her breath, carbon dioxide levels decrease, stimulating breathing by the brain stem.
D) as a child holds his or her breath, carbon dioxide levels increase, stimulating breathing by the brain stem.