May we leave the classroom now? No, you _____. You_____ to leave until the bell rings.
A:mustn't, are allowed
B:don't have to , are supposed
C:needn't , aren't allowed
D:can't , aren't supposed
如图所示的几何体,关于其结构特征,下列说法不正确的是( )
如图,OB是∠AOC的角平分线,OD是∠COE的角平分线,如果∠AOB=40°,∠COE=60°,则∠BOD的度数为( )
PM2.5日均值
(微克/立方米)
25,35
(35,45
(45,55
(55,65
(65,75
(75,85
频数
3
1
观察和实验是学习科学的重要方式,下列实验中观察到的颜色正确的是( )