下列图形属于棱柱的有( )
A:2个
B:3个
C:4个
D:5个
若x2-12-x÷2+xx+3有意义,则x的取值范围是 ____
双方的商讨已经破裂,哪一方应负责还不清楚。
Discussions between the two sides have ____ ____. It is not clear which side is ____ ____
目前人类已知的宇宙( )