问题
单项选择题 A1/A2型题
对潜影不起决定作用的因素是（）
A.被照体的原子序数
B.被照体的厚度
C.被照体的形状
D.X线的质与量
E.X线的散射线
答案
参考答案：C
解析：影响X线对比度（潜影）的因素：线吸收系数μ、物体厚度d、人体组织的原子序数Z、人体组织的密度ρ、X线波长λ。μd产生散射线使对比度受到损失。
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对潜影不起决定作用的因素是（）
A.被照体的原子序数
B.被照体的厚度
C.被照体的形状
D.X线的质与量
E.X线的散射线
参考答案：C
解析：影响X线对比度（潜影）的因素：线吸收系数μ、物体厚度d、人体组织的原子序数Z、人体组织的密度ρ、X线波长λ。μd产生散射线使对比度受到损失。
任务型阅读 Most schools are trying hard to improve their lunch programs and they want to offer the best food they can. Even if your school provides healthy options(选择)，you may still want to have something delicious outside. How do you take control? Take a packed lunch to school! Here are the four reasons to pack your lunch and snacks at least twice a week. Control Have you ever waited in the lunch line only to find when you get to the front that you don’t like what they’re serving? Variety If you’re eating the same food all the time , your body probably feels ready for a change. Packing lunch a couple of times a week means you can enjoy some favorites that you might not find at every school. Money Serving Packing healthy snacks so that you needn’t go out for a fast-food lunch, chocolate or a soda! If so, you will save much money. And you can buy something you need. Warm Feeling Remember when your mom or dad used to pack your lunch? Pack a lunch for yourself, maybe that is your favorite healthy food. Whether you pack or eat in the cafeteria(自助食堂)，what’s important is that you make right choices. If you are worried that cafeteria doesn’t offer enough healthy choices, try to make changes. Ask a teacher or someone in food service for advice on hoe to get started. Take a packed lunch to school
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