The purpose of contrast examination is to（）
A. increase the artificial contrast of organs and tissues
B. increase the density of organs and tissues
C. reduce the density of organs and tissues
D. increase the natural contrast of organs and tissues
E. change the structure of organs and tissues
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The penetrating power of X-rays in different parts of the body, arranged from strong to weak, are as follows（）
A. gas, fat, liquid and soft tissue, bone
B. gas, liquid and soft tissue, fat, bone
C. bone, fat, fluid and soft tissue, gas
D. fat, gas, liquid and soft tissue, bone
Which of the following methods of introducing contrast agents is incorrect（）
A. Inhalation
B. Oral
C. Perfusion
D. Puncture
E. Intravenous injection
The common mediastinal tumor in the hilum is___（）
A. lymphoma
B. teratoma
C. retrosternal goiter
D. thymoma
Which is not an X-ray finding of thymoma（）
A. Which is not an X-ray finding of thymoma
B. The mass is located in the middle of the anterior mediastinum
C. The mass is fusiform or flat
D. The outline of the mass is lobulated or wavy
E. There is multi-chamber calcification in the mass
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