Read the following passage and mark the letter A, B, C or D on your answer to indicate the correct word or phrase that best fits each of the numbered blanks from 25 to 29.

Mobile phones emit microwave radio emissions. Researchers are questioning whether exposure to these radio waves might lead to brain cancer. So far, the data are not conclusive. The scientific evidence does not (25) _____ us to say with certainty that mobile phones are categorically safe.On the other hand, current research has not yet proved clear adverse effect associated with the prolonged use of mobile phones.
Numerous studies are now going (26) _____ in various countries. Some of the results are contradictory but others have shown an association between mobile phone use and cancer. (27) _____, these studies are preliminary and the issue needs further, long - term investigation.
Until the scientific data is more definite, it is prudent for people to try not to use mobile phone for long (28) _____ 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 (29) _____ bodies are still growing may be at particular risk.