发生镜面反射的条件是:()
A.频率大于波长
B.引超反射的物体较小
C.反射面远大于声波波长
D.入射角与反射角之差大于45°
E.反射面不规则
参考答案:C
“教学相长”的故事启示我们[ ]
A.学生要始终听教师的话
B.老师是学生学习的榜样
C.师生间要相互学习、相互补充,共同提高
D.学生不能超过教师
— On summer nights, the weather is usually hot at night in the south of China.
— Yes, so I often go to sleep ______ the window ________.
A.let, open
B.with, opened
C.with, closed
D.with, open