[C] the use of cellular phones and cancer

    [D] mice exposed to cellular-phone radiation and the development of tumors

    22. “A clean bill of health” in the first paragraph means ________.

     [A] the money paid for a treatment in a hospital

     [B] a clean way of improving health

     [C] the health that is improved through good habits

     [D] a document of health stating the absence of disease

    23. According to the passage, radio waves are different from X rays in that ________.

     [A] the former are more dangerous

     [B] the former are a form of non-ionizing radiation

     [C] the latter are mainly used in hospitals

     [D] the latter are low-energy and low-heat signals

    24. The word “inconclusive” in the last paragraph means ________

     [A] disapproved by the public

     [B] not generally understood

     [C] misleading people to a conclusion

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