The word "odds" in Line 1 of Paragraph 1 means ______.

A．Getting too little sleep is the commonest sleep trouble with most Americans who have sleep trouble.
B．At least twenty percent of Americans don' t have enough sleep every night.
C．Our brains will force us to sleep when we have piled up too large a sleep deficit
D．Seven or eight hours of sleep every night is enough for people of different ages.

A．inform readers of Heller' s findings in his researches
B．persuade readers to get enough sleep at different ages
C．show readers the importance of getting enough sleep
D．tell readers how many hours of sleep they should get