I have a pencil case. It is nice and big. It has many colours. There are two blocks on my pencil case. One is yellow, the other is orange. In my pencil case, there are pens, pencils, a ruler and an eraser. I like my pencil case very much
水样 →加絮凝剂 沉降→过滤→吸附 →加消毒剂 自来水
如图是屋架设计图的一部分,其中∠A=30°,点D是斜梁AB的中点,BC、DE垂直于横梁AC,AB=16m,则DE的长为( )
一张圆形饭桌的面积是50.24平方分米,这张饭桌的直径是____分米?