Millions of people use contact lenses.For anyone who doesn’t mind sticking his fingers in his eyes,t——青夏教育精英家教网—

2.(★★★★★)Millions of people use contact lenses(隐形眼镜).For anyone who doesn’t mind sticking his fingers in his eyes,there are clear advantages:contacts correct vision better than glasses,are less often crushed underfoot,don’t make you look boring,and come in a huge variety of forms--soft,firm,colored,and even theatrical.

More and more people are turning to use of contact lenses.But are they safe?

Latest research from Australia shows that not all chemicals are effective in killing all germs(细菌)--and some of these germs can cause blindness in just 24 hours.

While most problems with contacts still can go back to poor hygiene(卫生)or overuse,not all sight-threatening conditions only happen to those who wash their lenses under the tap or decide,while tired and emotional,to sleep in their lenses for the third night running.

Two of the biggest eye-damaging killers--protozoan acanthamoeba and bacteria pseudomonas--are all around us,in our homes and water supplies.This seemingly harmless pair can cause blindness through keratitis(disease of the cornea).

“The cornea(角膜)is like a five-layered sandwich”,says Raymond Curran,a doctor from Omagh,Northern Ireland.“Once the bacteria get into a layer they can reproduce there and turn the cornea opaque(too dark to see through).”

An optician(验光师)may see one possibly sight-threatening case each month,but at an eye hospital there may be several each week.Acanthamoeba,often seemingly mild,can be misjudged until it is too late.Meanwhile,pseudomonas,more seriously,can cause increasing sight loss with each hour that passes.If not treated immediately,patients may need a corneal replacement.

And the really bad news,according to Professor Roger Buckley,at the Moorfields eye hospital in London,is that acanthamoeba is“one of the hardest germs on Earth”--it can survive in Antarctica.

Question 2:In the passage the writer mainly wants to tell us ________.

A.the possible danger of contacts

B.the importance of keeping contacts clean

C.some doctors’ opinions about contacts

D.the advantages and disadvantages of contacts

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5、过球面上三点的截面和球心的距离等于球半径的一半，且，则球的表面积为(　 )