Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrases that best fits each of the numbered blanks.

Mobile phones emit microwave radio emissions. Researchers are questioning whether exposure to these radio waves might (1) ______ to brain cancer. So far, the data are not conclusive. The scientific evidence does not enable us to say with certainly that mobile phones are categorically (2) ______. On the other hand, current research has not yet proved clear adverse effects associated with the prolonged use of mobile phones.

Numerous studies are now going (3) ______ in various countries. Some of the results are contradictory but others have shown an association between moblie phone use and cancer. (4) ______, these studies are preliminary and the issue needs further, long-term investigation.

Until the scientific data are more definite, it is prudent for people to try not to use mobile phones for long period of time. Don’t think that hands-free phones are any safer either. At the moment, research is in fact showing the opposite and they may be just as dangerous. It is also thought that young people (5) ______ bodies are still growing may be at particular risk.

(3)     A. on                             B. by                             C. through                     D. about