Two spherical bodies of mass $M$ and $5M$ and radii $R$ and $2R$ respectively are released in free space with initial separation between their centres equal to $12R$. If they attract each other due to gravitational force only, then the distance covered by the smaller body just before collision is:

1. A
   $2.5R$
2. B
   $4.5R$
3. C
   $7.5R$
4. D
   $1.5R$