Israeli researchers said they had identified a naturally produced compound that may explain why only some smokers get lung cancer.

　　Researchers found that smokers with low levels of the enzyme were five to 10 times more likely to develop lung cancer than smokers with the highest levels.

　　The enzyme fixes damage done to DNA by smoking and other environmental stresses and is one of a large group of repair compounds in the body.

　　Writing in the Journal of the National Cancer Institute, Zvi Livneh and his colleagues said 40 per cent of the 68 lung cancer patients they tested had low levels of enzyme activity, in contrast to 4 per cent of a healthy group of 68 people.

　　Non-smokers with the lowest levels of enzyme also had a higher risk of lung cancer, although their overall risk of cancer was much lower than that of the smokers.

　　Lung cancer is by far the biggest cancer killer in the world, killing a million people every year worldwide.

　　Smoking is also a major cause of heart disease and stroke. The researchers said the findings needed to be confirmed in larger studies but they may lead to the development of a blood test that smokers could take to determine their personal risk. 209

　　1. What is Israeli researchers’ discovery?

　　A. A naturally produced compound 

　　B. The possible reason for smokers to get lung cancer

　　C. A kind of new enzyme 

　　D. How lung cancer developed

　　2. According to the author, what is the function of the enzyme?

　　A. Repairing any damage. 

　　B. Damage done to DNA.

　　C. Causing environmental stresses. 

　　D. Repairing compounds in the body

　　3. How many people have been tested on levels of enzyme activity?

　　A. five to 10 times more 

　　B. 40 per cent

　　C. 68 

　　D. 136

　　4. The test also show that non-smokers

　　A. had the lowest levels of enzyme 

　　B. had a higher risk of lung cancer

　　C. had the risk of cancer as well