The school rules state that no child shall be allowed out of the school during the day, ________

accompanied by an adult.[ ]

A. once  

B. when

C. if  

D. unless

空间的形状是由其周围物体的边界所限定的，包括( )。

A．剖面形状与平面形状

B．具体形状与抽象形状

C．内部形状与外部形状

D．整体形状与局部形状