[多选题]掩护式支架的掩护梁与前后连杆组成的四连杆机构的作用包括（）。-我要搜题网

[单选题]托辊横向中心线与带式输送机中心线的不重合度不应超过
A.3mm;
B.6mm;
C.7mm;
D.8mm。

[不定项选择题]共用题干第三篇

Cell Phones : Hang Up or Keep Talking?

Millions of people are using cell phones today.In many places it is actually considered unusual not to
use one.In many countries,cell phones are very popular with young people.They find that the phones are
more than a means of communication一having a mobile phone shows that they are cool and connected.
The explosions around the world in mobile phone use make some health professionals worried.Some
doctors are concerned that in the future many people may suffer health problems from the use of mobile
phones.In England,there has been a serious debate about this issue.Mobile phone companies are worried
about the negative publicity of such ideas.They say that there is no proof that mobile phones are bad for your
health.
On the other hand,why do some medical studies show changes in the brain cells of some people who use
mobile phones?Signs of change in the tissues of the brain and head can be detected with modern scanning
（扫描）equipment. In one case , a traveling salesman had to retire at a young age because of serious memory
Loss.He couldn't remember even simple tasks.He would often forget the name of his own son.This man used
to talk on his mobile phone for about six hours a day,every day of his working week,for a couple of years.
His family doctor blamed his mobile phone use,but his employer's doctor didn't agree.
What is it that makes mobile phones potentially harmful?The answer is radiation.High-tech machines
can detect very small amounts of radiation from mobile phones.Mobile phone companies agree that there is
some radiation,but they say the amount is too small to worry about.
As the discussion about their safety continues,it appears that it's best to use mobile phones less often.
Use your regular phone if you want to talk for a long time.Use your mobile phone only when you really need
it.Mobile phones can be very useful and convenient,especially in emergencies.In the future,mobile phones
may have a warning label that says they are bad for your health.So for now,it's wise not to use your mobile
phone too often. The writer's purpose of wnting this article is to advise people__________.
A.to use mobile phones less often
B.to update regular phones
C.to stop using mobile phones
D.to buy mobile phones

[多选题]掩护式支架的掩护梁与前后连杆组成的四连杆机构的作用包括（）。A.直接承受冒落矸石的载荷B.直接承受顶板通过顶梁传递的水平载荷引起的弯矩C.防止冒落矸石动支架后部窜入架间和工作面D.有利于支撑顶板

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[多选题]掩护式支架的掩护梁与前后连杆组成的四连杆机构的作用包括（）。
A.直接承受冒落矸石的载荷
B.直接承受顶板通过顶梁传递的水平载荷引起的弯矩
C.防止冒落矸石动支架后部窜入架间和工作面
D.有利于支撑顶板