一个圆的半径如果由3厘米增加到5厘米,那么圆的周长就增加
A:4厘米
B:2厘米
C:12.56厘米
D:31.4厘米
阅读下图,回答问题。
____Shall we play in the playground?
____Can I learn to use the computer?
____Would you like to come here?
____What would you like for your birthday?
A. Sure.
B. Yes, I'd love to.
C. OK, let's go.
D. It's a secret.
求下面三角形的面积.
面积是____ dm2