People who suffer from attention-deficit/hyperactivity disorder (adhd) tend to have unusually low levels of select one: a. dopamine b. epinephrine c. norepinephrine d. gamma-aminobutyric acid (gaba)

People who suffer from attention-deficit/hyperactivity disorder (ADHD) tend to have unusually low levels of dopamine.  

ADHD is a brain disorder characterized by problems in paying attention and excessive activity and it is suggested that lower levels of dopamine (elevated number of dopamine transporters) are associated with symptoms of ADHD. ADHD is associated with functional impairments of dopamine pathways and also norepinephrine pathways because these pathways are responsible for modulating executive function (cognitive control of behaviour).

1.989×10^30 kg is the weight of the sun.