A special lab at the University of Chicago is busy only【C1】______.It is a dream【C2】______where researchers are at work【C3】______dreamers.Their findings have concluded that【C4】______dreams from three to seven times each night，【C5】______in ordinary life a person may【C6】______none or only one of his dreams.
While the【C7】______sleep，special machines【C8】______their brain waves and eye movements as well as the body movements that【C9】______the end of a dream.Surprisingly，all subjects【C10】______soundly.
【C11】______say that a person usually fidgets before a dream.【C12】______the dream has started，his body relaxes and his eyes【C13】______more active，as if the curtain【C14】______on a show.When the machine【C15】______that the dream is over，a buzzer wakes the【C16】______He sits up，records his dream，and goes back to sleep perhaps to【C17】______some more.
Researchers have found that if the dreamer，is【C18】______immediately after his dream，he can usually recall the entire dream，If he is allowed to sleep even【C19】______his【C20】______of the dream will have faded.

【C1】（）

A．at noon
B．in the morning
C．at night
D．in spring