What happens next in this paragraph?

How to take melatonin
Know how melatonin works.
Melatonin is a natural hormone produced by your pineal gland located in your brain. It acts like a neurotransmitter, or chemical messenger, to activate certain pathways in your brain.
Possible answers:
(A). It forms an barrier between your brain cells and the body that's responsible for producing melatonin hormone. You'll find that getting regular periods to regulate your mood can prevent you from being able to follow a normal schedule.;
(B). If you don't take melatonin, it can suppress the melatonin secretion. The hpv vaccine (ive) is the first dose for 30 people to develop melatonin.;
(C). Once this phase begins, your brain reacts with melatonin and shifts up from there, producing pain and a neurotransmitter. These neurotransmitters are thought to relieve symptoms, but melatonin has drawbacks as well.;
(D). Its role in establishing a sleep cycle has been recognized; however, recent research indicates it may be involved in other body functions as well. In the usa, melatonin is available over-the-counter as a dietary supplement and is therefore not regulated by the fda.;
(D).