Perhaps you’ve visited a restaurant and seen clear, water-filled bags hanging on the doors．You might ask，“What’s all this about? Some crazy new way to control temperature?A method of saving money on water containers?”While any effect on temperature is purely accidental，these hanging bags are all about driving pests away．
The water bag method to drive flies away has many supporters So how does the method drive flies away?Some insist the flies regard the clear liquid as the surface of a body of water．Others think the insect flies away at the sight of its own big reflection．But the most popular reasoning that exists among scientists is light refraction(折射)．
The insect’s fiead mostly consists of a pair of large complex eyes，each of which is made up of 3，000，to 6,000 simple eyes．These eyes can’t focus on objects like human eyes，instead they provide the fly with a mosaic(拼凑的)view of the world around them．A housefly bases its sense of direction on the sunlight．Some scientists believe that when these complex and sensitive eyes experience refracted light，the insect becomes confused and flies away．
Plenty of people don’t think water bags can keep flies away．Mike Stringham，a professor，conducted a 13-week field trial on two egg farms．He concluded those areas equipped with water bags actually experienced higher levels of housefly activity．Its purpose was to determine whether the water bags could be used to decrease fly populations on egg farms．
So do bags of water lower the number of houseflies around homes and restaurants? There are reasonable explanations that argue yes and strong evidence that proves no．Anyway，you can still find water bags hanging near restaurants and backyards across the globe．

Some restaurants hang water-filled bags on the doors to ____________．

A．control temperature	B．get hot water
C．save money	D．drive flies off

What is considered more reasonable about the water bag method?

A．The light refraction of the bag drives flies away．

B．Flies are frightened away by their own reflections．

C．Flies mistake the bags as the surface of the waters．

D．The heat of the bags by the sunlight keeps flies off．

What is Paragraph 3 mainly about?

A．How many eyes a fly has．

B．How flies focus on objects．

C．Where flies can get sunlight．

D．Why refracted light keeps flies away．

We can describe the water bag method as“______________．”

A．practical	B．useless
C．controversial	D．Ridiculous