A:铁丝在空气中剧烈燃烧,火星四射
B:硫在空气中燃烧产生明亮的蓝紫色火焰
C:向硫酸铜溶液中滴加氢氧化钠溶液产生蓝色沉淀
D:红磷在氧气中燃烧产生大量白色烟雾
食物的消化靠消化系统来完成的,它由____和____组成.
列光现象中,由于光的折射引起的是( )
在等式□×24+□×30=27,□里可同时填( )
-- Do you know ______ our Chinese National Symbol of Day (国家公祭日) is?
-- Yes, it's on December 13th. It's in memory of the people_____ were killed in Nanjing Massacre.