题目内容

Listen! The students their campus song together in the classroom

A. singing
B. sing
C. are singing
D. issinging

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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

光栅衍射用的是光的什么原理

A. 光沿直线传播
B. 光的偏振
C. 光的叠加
D. 光的干涉