某土天然体积$V_1=100\,\mathrm{m}^3$，开挖后松散体积$V_2=120\,\mathrm{m}^3$，则$K_s$为？

1. A

   $0.83$

2. B

   $1.20$

   正确
3. C

   $1.50$

4. D

   $20$