In temperate regions the growth rings on turtles’ epidermal plates reflect seasonal variations in growth.

单项选择题The study was the first to tell the difference between 7 and 8 hours of sleep a night.

单项选择题More than 1.1 million Americans participated in the six-year study.

单项选择题All the participants were from the state of California.

单项选择题The study shows that the longer you sleep each night, the longer you’ll live.

单项选择题The findings indicate that it is all right to sleep for 6.5 hours a night.