多项式1+2xy﹣3xy2的次数为( )
A:1
B:2
C:3
D:5
下列关于碳及其氧化物的说法中,正确的是( )
It is ______for him to get to school on time, because it is raining ______.
下列有关大肠杆菌的叙述错误的是( )