Dogs might have the latest tools in the fight against cancer （癌症）：their noses!Researchers at California's Pine Street Foundation （PSF） say they have trained five dogs to smell cancer on a prison's breath.This could be exciting news.

   A dog's sense of smell may be 10，000 to 100，000 times stronger than ours.But can dogs really smell illness？PSF researcher Michael McCulloch says yes. "We were very surprised by how exact they were，" he said. "They were telling who had cancer，and they were also saying who didn't."

    McCulloch and his team asked four healthy people and one with cancer to blow into plastic tubes （塑料管）.Special materials in the tubes kept the things of each breath.The tubes were then placed one yard apart.Finally the dogs were allowed to smell the tubes.Each dog had been trained for three weeks to sit when it smelled cancer.Ninety﹣nine percent of the time，the dog sat next to the tubes blown into by patients with lung cancer.The dogs were right 88 percent of the time about breast cancer.

Dogs in the Pine Street Foundation test were trained to sit when they smelled cancer.How well did they perform？Take a look at this chart to find out.
Breath Sample	Number of Times the Dogs Sat Down	Number of Times the Dogs Kept Standing
Breath from lung cancer patients	564	10
Breath from healthy persons	4	720

No lab test for cancer has given more correct results than this test.The results are so amazing that many experts question the dogs' smelling power.They wonder if there were other reasons why the dogs did so well.For example，they thought the way the dog trainers behaved could have influenced how the dogs acted.However，most experts agree that this study is important.The information could help scientists create a simple breath test for cancer in the future.Once again humans may be getting a helping paw or nose﹣from their best animal friends.

（1）What's the latest tool a dog might have in the fight against cancer？ 　 　

A.Tooth.

B.Nose.

C.Ear.

（2）What happened first in the Pine Street Foundation test？ 　 　

A.The dogs were trained.

B.The tubes were placed one yard apart.

C.The dogs smelled the tubes.

（3）What was a dog supposed to do when it smelled cancer？ 　 　

A.Smell again.

B.Turn around.

C.Sit down.

（4）Look at the chart.How many times did the dogs keep standing when they smelled the breath from healthy persons？ 　 　

A.Less than 10 times.

B.Almost 600 times.

C.About 700 times.

（5）Why do many experts question the dog's smelling power？ 　 　

A.Because no lab test for cancer has given more correct results.

B.Because the dog trainers influenced how the dogs acted.

C.Because they don't think this study is important.