15 + 14 = 75×20%= 45 × 716 = 920 × 518 =
3.14×3= 58 ÷ 14 = 15.7÷5= 20÷ 14 =
18 - 116 = 49÷ 714 = 81× 29 = 56× 57 =
1- 25 = 34 + 45 = 84×50%= 25 ×40=
如图表示人体某种免疫过程.下面有关叙述正确的是( )
体积相同的甲乙两物体质量之比为2:5,甲的密度与乙的密度的比是( )