Although children believe that "holding my breath until I die" is possible, why should parents not be concerned by this threat?

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.