A:7π
B:25π2
C:12π
D:25π
Tim:Yes,I have an e-friend in the US.His name is David.He is 15 years old.He is a____student.
—Er , I see. I will do it myself.
“千里之行,始于足下”这句名言告诉我们:培养和锻炼意志要( )
①扩大养猪规模 ②获利减少 ③减小养猪规模 ④获利增加