下面的短文后有2项测试任务：(1)第23～26题要求从所给的6个选项中为第2～7段名其中4段选择1个最佳标题；(2)第27～30题要求从所给的6个选项中为每个句子确定1个最佳选项。 Screen Test 1．Every
year millions of women are screened with X-rays to pick up signs of breast
cancer. If this happens early enough, the disease can often be treated
successfully. According to a survey published last year，21 countries have
screening programmes. Nine of them, including Australia, Canada, the US and
Spain, screen women under 50. 2．But the medical benefits of screening these
younger women are controversial，partly because the radiation brings a small risk
of inducing cancer. Also, younger women must be given higher doses of X-rays
because their breast tissue is denser. 3．Researchers at the Polytechnic
University of Valencia analysed the effect of screening more than 160,000 women
at 11 local clinics. After estimating the women’s cumulative dose of radiation,
they used two models to calculate the number of extra cancers this would
cause. 4．The mathematical model recommended by Britain’s National
Radiological Protection Board(NR- PB)predicted that the screening programme
would cause 36 cancers per 100,000 women,18 of them fatal. The model preferred
by the UN Scientific Committee on the Effects of Atomic Radiation led to a lower
figure of 20 cancers. 5．The researchers argue that the level of
radiation-induced cancers is "not very significant" compared to the far larger
number of cancers that are discovered and treated. The Valencia programme，they
say，detects between 300 and 450 cases of breast cancer in every 100,000 women
screened. 6．But they point out that the risk of women contracting cancer from
radiation could be reduced by between 40 and 80 percent if screening began at 50
instead of 45,because they would be exposed to less radiation. The results of
their study, they suggest, could help "optimize the technique" for breast cancer
screening. 7．"There is a trade-off between the diagnostic benefits of breast
screening and its risks." admits Michael Clark of the NRPB. But he warns that
the study should be interpreted with caution."0n the basis of the current data,
for every 10 cancers successfully detected and prevented there is a risk of
causing one later in life. That’s why radiation exposure should be minimized in
any screening programme. Paragraph 2______