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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。

{{B}} Screen Test{{/B}}
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 o