If ${\mathrm{I}}_1\text{ and }{\mathrm{I}}_2$ be the size of the images respectively for the two positions of lens in the displacement method, then the size of the object is given by 

• A

  $\frac{{\mathrm{I}}_1}{{\mathrm{I}}_2}$

• B

  ${\mathrm{I}}_1\times {\mathrm{I}}_2$

• C

  $\sqrt{{\mathrm{I}}_1\times {\mathrm{I}}_2}$

• D

  $\sqrt{\frac{{\mathrm{I}}_1}{{\mathrm{I}}_2}}$