X线胶片上的黑白差别，取决于
A．组织的密度差别，而不是厚度差别
B．组织的厚度差别，而不是密度差别
C．组织的X线吸收量的差别，与吸收率无关
D．组织的X线吸收率的差别，而不是吸收量的差别
E．组织的密度差别和厚度差别
参考答案：E
解析：X线的穿透性是X线成像的基础，X线穿透物体的程度与物体的密度和厚度相关。密度高，厚度大的物体吸收的多，通过的少。X线可穿透可见光不能穿透的物体，在穿透过程中有一定程度的吸收即衰减，吸收多时，显示为胶片上的白色，反之为黑色。
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| Many animals use some kind of "language " They use singals that have meanings. For example, when a bee has found some food, it goes 1 its home. It’s 2 for a bee to tell 3 bees where the food is by speaking to 4 , but it can do a little dancing. This tells the bees where the food is and 5 it is. Some animals show how they feel by making sounds. It’s not difficult to tell if a dog is angry 6 it barks.Birds made several different sounds and 7 has its own meaning. Sometimes we human make sounds 8 we make sounds like“Oh!” or “Ouch!” to show how we feel about something or when we 9 something on our feet. We humans have languages. We have words. These words have the meaning of things. actions, feelings or ideas. We 10 give each other information. By writing down words, we can remember what has happened or send messages to people far away. | |||
| ( )1. A. out of ( )2. A. important ( )3. A. each other ( )4. A. it ( )5. A. how long ( )6. A. so that ( )7. A. each ( )8. A. in the same sound ( )9. A. put ( )10. A. able to | B. on with B. difficult B. another B. him B. how far away B. before B. every B. by the different sound B. drop B. are able to | C. away from C. necessary C. the other C. them C. how many C. until C. all C. in the same way C. fall C. are able | D. back to D. impossible D. others D. themselves D. how old D. because D. some D. by the different way D. set D. be able to |