It might be fun to use your smartphone， but be careful． Too much screen time may be harmful to your health．

First， it is bad for your eyes． A researcher called Sarah Hinkley says the problem comes from the blue light that the screen gives out． Looking at a smartphone for a long time can cause eye strain（劳损），headaches and dry eyes． So it is a good idea to take a break every 15 minutes when you are working at a computer or using a smartphone

Second， screen use can do harm to children's brains． A new study shows that using screens too much can affect（影响） how children's brains grow． If children use screens for more than one hour a day， they might have lower levels of white matter in their brains． White matter is a key to the development of language and reading skills．So it is wise to cut down the time of children using all kinds of screens．

Third， using screens too much will affect your sleep． According to a study， about 95% of the people between the ages of 13 and 64 use electronics before bed， especially the young people under 20． Doctors say that the light from those electronics at night may make you excited before you go to bed． Then it's hard for you to get enough sleep． So you'd better turn off smartphones，TVs， and all other screens an hour before your bedtime．

To keep healthy， doctors and researchers strongly advise that you shouldn't use screens for long hours．

（1）The blue light from your screens can cause 　　．

A．	eye strain
B．	headaches
C．	dry eyes
D．	all of the above

（2）According to the passage， you can't sleep well because you 　　．

A．	take a break every 15 minutes
B．	have lower levels of white matter
C．	use screens too much before bed
D．	are the people from 13 to 64

（3）Which of the following is NOT true according to the passage？ 　　

A．	Using smartphones for long hours does harm to your eyes．
B．	A lot of screen time affects children's brain growth．
C．	The light from electronics at night may make you excited．
D．	People of all ages mustn't use electronics．

（4）You may read the passage in 　　．

A．	a science magazine
B．	a travel diary
C．	a guide book
D．	a novel

（5）What is the main idea of the passage？ 　　

A．	The ways to keep healthy．
B．	The harm of using screens too much．
C．	The ways to use screens．
D．	The advantages of using screens．