Iin a bar for the summer.
A. working
B. am working
C. work
D. have been working
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Listen! The students their campus song together in the classroom
A. singing
B. sing
C. are singing
D. issinging
My mother a dress when she cuts her finger.
A. is maken
B. is making
C. makes
D. has maken
Look! The boy football with his classmates on the playground.
A. is playing
B. is being played
C. plays
D. has played
衍射光栅的质量主要看哪个指标
A. 光栅常数
B. 光栅宽度
C. 光栅厚度
D. 光栅的颜色
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