Conjoined Twins, Whose Bodies Are Joined at Birth, Have Shown

Conjoined twins, whose bodies are joined at birth, have shown that

A) when one twin is asleep, the other one must also be asleep due to the sleep-promoting chemicals in the connected bloodstreams.
B) when one twin is asleep, the other one must also be asleep because of the decreases in blood pressure across their connected systems.
C) it is not unusual for one twin to be asleep while the other one is awake.
D) irregular sleeping patterns occur due to the connected systems which cause a disruption in the balance of the sleep-promoting chemical found in their connected bloodstreams.