A:C3H8
B:C4H8
C:C5H8
D:C7H8
—It's____(June 29th/Monday). It's the____(first/second)day of a week.
下列计算中,错误的是( )
C3N4是一种新型材料,它的硬度比金刚石还大,可用作切割工具。在C3N4中C元素的化合价为+4,则N元素的化合价是( )