Read the paragraph. American teens are sleep-deprived. Studies have shown that teenagers need, on average, about nine hours of sleep a night. To accomplish this and still get to school on time, most teens would need to get to bed no later than 9:30 P.M. each evening. However, studies also show that biological changes associated with adolescence actually make it harder for teens to fall asleep before 11 P.M. Additionally, teenagers lead very busy lives, making an earlier bedtime difficult. Most have homework, part-time jobs, extracurricular activities, and an active social life. The nature of their lifestyles often keeps teens up late and contributes to their sleep deprivation. Which identifies the topic sentence of this paragraph?
Studies have shown that teenagers need, on average, about nine hours of sleep a night.
However, studies also show that biological changes associated with adolescence actually make it harder for teens to fall asleep before 11 P.M.
Additionally, teenagers lead very busy lives, making an earlier bedtime difficult.
American teens are sleep-deprived.