Keeping a pet cat puts owners at a greater risk of going blind，but a dog appears to protect eyesight，a new study suggests.
Scientists have discovered that dogs and cats carry antigens（杭原）which can cause different immune responses（免疫反应）in humans. While the allergen（过敏原）which dogs carry reduces the chance of developing glaucoma（青光眼）一the second leading cause of blindness in the UK--- owning a cat nearly doubles the risk of getting the eye disease.
Many pet owners suffer allergic reactions to their pets but still choose to keep them. However， the new study suggests that even a small immune response could lead to blindness. The study by the University of California，Los Angeles，found that cat owners who reacted to their pet allergen had a 90 percent increased risk of glaucoma compared with non-pet owners. But dog owners were 20 percent less likely to get the disease.
Keeping a dog also has the added benefit that owners are outside more which helps to protect against short-sightedness.
"Not only is a dog man’s best friend，he may also save your sight，”said British laser eye surgeon Dr David Allamby. "Cats could cause our immune system to react in a way that leads eyes to the development of glaucoma. Exposure（接触）to dogs appears to be linked to the opposite effect and could be protective against the disease."
The researchers believe that dogs are healthier for humans because they spend more time out-doors
"The protective effect of dogs could be due to their natural antigens in their dead skin，but might also be because they spend more time outdoors and are happy to get dirty，whereas cats are cleaner animals." said Dr Anne Coleman，of University of California，Los Angeles.
21．The purpose of the text is to
A. make pet dogs popular.
B. advise people to abandon their cats.
C. share a new study result.
D. call on pet owners to spend more time outside with their pets
22. Which of the following statements is TRUE according to the article？
A. Glaucoma is the first leading cause of blindness in the UK.
B. Dogs are healthier for humans because they are man’s best friends.
C. Owning a cat nearly has the same risk of getting glaucoma compared with owning a dog.
D. Dog owners are outside more which is good for their eyesight protection.
23．In which part of a magazine can we most probably read this article？
A. Health B. Science C. Business D. Entertainment
答案 21—23 CDB