阅读下面这篇短文，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2～5段每段选择1个正确的小标题；(2)第27～30题要求从所给的6个选项中选择4个正确选项，分别完成每个句子。 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 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 (NRPB) 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 eases 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. “On 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 ______