[单选题]
Substance A has a den1r9zs38)nkpry + on rxsity 3wn8q4t4) l a6 7-ggkv(sm vfmi6lwzxof $3.0 \; g/cm^{3}$ 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
