15．Experts recently suggested that teens should start adopting early bedtimes．Before you dismiss it as a habit suited only for young kids，consider that there are serious advantages in being well-rested．And now，even more research suggests that putting phones away before going to sleep is important to teens'well-being．
A new study from Seton Hall University School of Health and Medicine Science found that 62percent of kids used their smart phones before bed，and it's causing less sleep and poor performance in school．
Those teens who text（发短信） before bedtime tend to go to sleep later，and get up later in the morning．Such behavior can be associated with mental health issues like depression or anxiety．Besides，once teens do receive a text，experts found，they tend to respond right away．Then the text conversation continues----resulting in an even later bedtime．
The study's co-author Dr．Peter Polos says this leads to excessive stimulation（过度刺激） at night．Light from electronic devices can block the secretion（分泌） of melatonin---a hormone（荷尔蒙） that promotes sleep，which makes sleep difficult in the face of overuse of smart phones at night．It's true!More screen time means less sleep time； other studies have suggested the same idea．
As for a final piece of advice，Dr．Sushanth Bhat says，since getting the proper amount of sleep is very important for brain development and learning in the teenage years，our study should encourage parents and guardians （监护人） to limit adolescent smart phone usage at night．Keep in mind that teens aren't the only ones addicted to their phones!Adults can also benefit from setting a tech curfew（宵禁） for themselves．After all，kids learn by example!
32．What is the text mainly about？D
A．How to promote sleep．
B．How kids learn from their parents．
C．The advantages of going to bed early．
D．The disadvantages of phone usage before bed．
33． Who are likely to go to sleep later according to the text？A
A．Kids having text conversations before bed．
B． Kids putting their phones away at night．
C．Kids studying their lessons hard at school．
D．Kids exercising with friends after school．
34．Melatonin canC．
A．make sleep difficult
B．lead to later bedtimes
C．help people fall asleep
D．wake people from a sleep
35．The author advises parents toC．
A．learn from their kids
B．get rid of smart phones
C．set a good example to their kids
D．try to benefit from hi-tech development．
