Tom didn't go hiking with his classmates ____ his illness.
A:because
B:because of
C:as
D:since
____的世纪 ____的发现
____的神仙 ____的生活
只用水不能区分各组物质(物质均为固体)的是( )
我国煤炭、石油都丰富的地区是( )