English keeps _________ all the time.
A. change
B. changing
C. to change
D. changed
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Is English _______ for the job?
A. must
B. need
C. a must
D. a need
He spent a lot of time ________ English these days.
A. study
B. to study
C. is studying
D. studying
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