A:Who is that girl ?
B:What's her name ?
C:What does he do?
如图甲所示,凹面镜对光线有会聚作用.
23 ×15=
0.324÷0.01=
4÷ 49 =
109 ×1 45 =
0× 23 ÷3=
3.2x﹣1.9x=
2a+1.5a=
24×4%=
1.25×25×8×0.4=
( 23 ﹣ 19 )×18=