Agriculture is the country's chief source of wealth, wheat______ by far the biggest cereal
A. is
B. been
C. be
D. being
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The focus of this book is to develop ______.
A. writing skill
B. reading skill
C. speaking and listening skills
D. listening, speaking, reading and writing skills
两束频率相同、振动方向相同、传播方向相反的单色光波叠加后将会产生驻波现象。
A. 正确
B. 错误
在平行平板的双光束干涉中，干涉定域面位于无穷远处；平板越厚，中心条纹的干涉级次越高；入射光波长越长，条纹间隔越稀。
A. 正确
B. 错误
According to the passage, your persona is______.
A. your unconscious self
B. your innermost self
C. a hypocritical appearance
D. your variable mask presented to others
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