Many doctors and scientists believe that there are different causes for the different forms of cancer. Working conditions may __51__ cancer. For example, people who work in __52__ contact with chemical compounds like arsenic or asbestos may develop cancer. People who work for long periods of time with X-rays or radioactive material may get leukemia or cancer of the skin, bone or lungs. Smoking is __53__ cause of cancer. Many experiments have shown that smoking can produce lung cancer as well as cancer of the mouth, larynx and esophagus. __54__, viruses may cause cancer. Scientific research has shown that viruses bring about certain kinds of cancer in laboratory animals. Scientists are now trying to find out __55__ true for humans as well. Although we don,t have the answer yet, perhaps in the near future we will know what causes this disease.
【題組】53.
(A) other
(B) the other
(C) another
(D) one