Since the late l970s，there has been lively debate about the possible connection between overhead power lines and childhood cancer．More specifically，researchers have been interested in the link，if any， between the extremely low frequency magnetic fields generated by these lines and childhood leukaemia．④ Studies on people have left more questions than answers， and laboratory experiments have failed to pin down a Dlausible mechanism whereby weak magnetic fields could trigger the disease．②In this context，a paper in this week’s issue of the British Medical Journal may well spark alarm．But it shouldn’t．
Gerald Draper and his colleagues at the University of Oxford，and John Swanson of National Grid Transc0，a Dower．transmission company，have looked at the distribution of childhood cancer along the Dower lines of the national electricity grid in England and Wales．The group analysed more than 2 9，000 cases of children with cancer against a comparable group without the disease．They found that children whose homes when they were born were within 200 metres of high—voltage lines appeared to have a 70％ higher risk of leukaemia——but not other cancers--than those who lived more than 600 metres from the lines．If living Bear power lines does increase the risk of cancer，the researchers reckon their result would account for about five of the more than 400 cases of childhood leukaemia that occur in England and Wales each year．④Even that small number is a big if．
Other studies that have shown a correlation between childhood leukaemia and power lines have done so onlv at smaller distances from the lines than Dr Draper’s group．⑤Indeed，the researchers reckon the magnetic fields at the distances they considered are less than the average fields in homes--and fields of this level have been shown to have no effect．“We have no satisfactory explanation for our results in terms of causation by magnetic fields，and the findings are not supported by convincing laboratory data or any accepted biological mechanism”．they damply conclude．
Correlations are tricky things．Childhood leukaemia probably involves damage to DNA before birth． But that damage can be caused in many ways--infection，chemicals and ionizing radiation,for example． Despite Dr Draper’s study，current evidence does not prove that living by high-voltage lines should be added to this list． [381 wordsl
1．By saying“a paper…may well spark alarm”，the author means that______．
A．the mechanism formulated in the paper is still plausible
B．the achievements introduced in the paper are unexpected
C．shocking influence of power lines might be revealed in the paper
D．readers should be welI prepared for the alarm before reading the paper
2．The researchers in Dr Draper’s group______．
A．were most experts of fl power—transmission company
B．investigated more than 400 cases of childhood cancer
C．studied the power lines of the nationaI electricity grid
D．found a link between power lines and childhood leukaemia
3．The comment“Even that small number is a big if”probably means that______．
A．the real number of cancer cases caused by power lines is negligible
B．the real number of cancer cases caused by power lines is much larger
C．1iving near power lines doesn’t necessarily increase the risk of cancer
D．there are more cases of childhood leukaemis outside England and Wales
4．The author maintains that______．
A．a(chǎn)ny two things in the world might be correlated
B．the link between power lines and cancer is uncertain
C．strong magnetic fields are likely to trigger childhood cancer
D．there is no link between power lines and childhood leukaemia
5．It is implied in the text that the link between power lines and childhood leukaemia．examda.
A．there is little evidence to prove
B．Dr Draper’s group has verified
C．a(chǎn) plausible mechanism can justify
D．further evidence is needed to support
Gerald Draper and his colleagues at the University of Oxford，and John Swanson of National Grid Transc0，a Dower．transmission company，have looked at the distribution of childhood cancer along the Dower lines of the national electricity grid in England and Wales．The group analysed more than 2 9，000 cases of children with cancer against a comparable group without the disease．They found that children whose homes when they were born were within 200 metres of high—voltage lines appeared to have a 70％ higher risk of leukaemia——but not other cancers--than those who lived more than 600 metres from the lines．If living Bear power lines does increase the risk of cancer，the researchers reckon their result would account for about five of the more than 400 cases of childhood leukaemia that occur in England and Wales each year．④Even that small number is a big if．
Other studies that have shown a correlation between childhood leukaemia and power lines have done so onlv at smaller distances from the lines than Dr Draper’s group．⑤Indeed，the researchers reckon the magnetic fields at the distances they considered are less than the average fields in homes--and fields of this level have been shown to have no effect．“We have no satisfactory explanation for our results in terms of causation by magnetic fields，and the findings are not supported by convincing laboratory data or any accepted biological mechanism”．they damply conclude．
Correlations are tricky things．Childhood leukaemia probably involves damage to DNA before birth． But that damage can be caused in many ways--infection，chemicals and ionizing radiation,for example． Despite Dr Draper’s study，current evidence does not prove that living by high-voltage lines should be added to this list． [381 wordsl
1．By saying“a paper…may well spark alarm”，the author means that______．
A．the mechanism formulated in the paper is still plausible
B．the achievements introduced in the paper are unexpected
C．shocking influence of power lines might be revealed in the paper
D．readers should be welI prepared for the alarm before reading the paper
2．The researchers in Dr Draper’s group______．
A．were most experts of fl power—transmission company
B．investigated more than 400 cases of childhood cancer
C．studied the power lines of the nationaI electricity grid
D．found a link between power lines and childhood leukaemia
3．The comment“Even that small number is a big if”probably means that______．
A．the real number of cancer cases caused by power lines is negligible
B．the real number of cancer cases caused by power lines is much larger
C．1iving near power lines doesn’t necessarily increase the risk of cancer
D．there are more cases of childhood leukaemis outside England and Wales
4．The author maintains that______．
A．a(chǎn)ny two things in the world might be correlated
B．the link between power lines and cancer is uncertain
C．strong magnetic fields are likely to trigger childhood cancer
D．there is no link between power lines and childhood leukaemia
5．It is implied in the text that the link between power lines and childhood leukaemia．examda.
A．there is little evidence to prove
B．Dr Draper’s group has verified
C．a(chǎn) plausible mechanism can justify
D．further evidence is needed to support