Dogs are known for their sense of smell．They can find missing people and things like bombs and illegal drugs．Now a study suggests that the animal known as man’s best friend can even find bladder（膀胱）cancer．
Cancer cells are thought to produce chemicals with unusual odors（气味）．Researchers think dogs have the ability to smell these odors, even in very small amounts, in urine（尿）．The sense of smell in dogs is thousands of times better than in humans．
The study follows reports of cases where, for example, a dog showed great interest in a growth on the leg of its owner．The man was later found to be skin cancer．Carolyn Willis led a team of researchers at Amersham Hospital in England．They trained different kinds of dogs for the experiment．The study involved urine collected from bladder cancer patients, from people with other diseases and from healthy people．Each dog was tested 8 times．In each test there were 7 samples for the dogs to smell．The dog should signal the one from a bladder cancer patient by lying down next to it．Two cocker dogs were correct 56 percent of the time．But the scientists reported an average success rate of 41 percent．The British Medical Journal published the research．In all, 36 bladder cancer patients and 108 other people took part．During training, all the dogs reportedly even identified（认出）a cancer in a person who had tested healthy before the study．Doctors found a growth on the person’s right kidney（肾）．Carolyn Willis says dogs could help scientists identify the combined chemicals produced by bladder cancer．That information could then be used to develop machines to test for the chemicals．The team also plans to use dogs to help identify markers for other kinds of cancer．
49．What’s the general idea of the text?
A．Dogs have a good sense of smell        B．Dogs can help cure cancer
C．Dogs can smell cancer                 D．Dogs help perform experiments
50．According to the text, people who suffer bladder cancer_____
A．often have urine with unusual smell                       B．probably smoke cigarettes in their life
C．can easily make dogs lie down                    
D．are likely to die within nine years
51．The underlined word “involved” in the text is closest in meaning to _____．
A．showed            B．used          C．proved       D．preferred
52．What can we conclude from the last paragraph?
A．Dogs can only smell bladder cancer．
B．Dogs have a good knowledge of cancer．
C．Cancer doesn’t have any sign in the beginning．
D．Scientists might invent some equipment to test cancer．