[单选题]
Substance A has a densitdx, +dny9 )ri2cix1cmk s)e g2y os8b 0xp i1u5zl 4zf+fcf $3.0 \; g/cm^{3}$ and substance B has a density of $4.0 \; g/cm^{3}$. In order to obtain equal masses of these two substances, the ratio of the volume of A to the volume of B will be equal to
