-The people studied by the researchers………

***A)participated in the experiment at their own will

B)suffered from insomnia

C)were having difficulty getting up early

D)were unable to wake up by other means

E)came from similar backgrounds

A)exists in higher levels in people who wake up very early

***B)is produced by the body some time before a person wakes up

C)can't be measured without waking up the person being studied

D)is used by doctors for people who have difficulty getting up

E)is responsible for causing sleeplessness in a number of people