A charge Q is distributed uniformly in a sphere (solid). Then the electric field at any point r where r < R (r is radius of sphere) varies as : 

• A

  ${\mathrm{r}}^{1/2}$

• B

  ${\mathrm{r}}^{-1}$

• C

  r

• D

  ${\mathrm{r}}^{-2}$