He spent a lot of time ________ English these days.
A. study
B. to study
C. is studying
D. studying
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In some Western countries, people try ______a black cat.
A. to avoid
B. avoid
C. avoiding
D. avoided
X线影像的转换介质，不包括
A. 屏-片系统
B. 影像增强器
C. 荧光屏
D. 滤线栅
医用X线胶片属于
A. 复性感光材料
B. 正性感光材料
C. 银盐感光材料
D. 非银盐感光材料
感绿胶片的吸收光谱的峰值在
A. 500nm
B. 550nm
C. 600nm
D. 650nm
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