Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks from 31 to 35.

Mobile phones emit microwave radio emissions. Investigators are questioning whether exposure to these radio waves might (31) _______ to brain cancer. So far, the figures are not final. The precise evidence does not enable us to say in certain that mobile phones are definitely safe. On the other hand, recent research has not yet (32) ________ clear adverse effect associated with the prolonged use of mobile phones.

Many studies are now going (33) _______ in numerous countries. Some of the results are contradictory but others have shown an association between mobile phone use and cancer. However, these studies are preliminary and the issue needs further, long - term investigation.

(34) ________ the scientific data is more definite, it is advisable for people to try not to use mobile phone for long periods 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 hazardous. It is also thought that young people (35) ________ bodies are still growing may be at particular risk.