The figure shows a circuit diagram of a Wheatstone bridge to measure the resistance G of the galvanometer. The relation $\frac{\mathrm{P}}{\mathrm{Q}}=\frac{\mathrm{R}}{\mathrm{G}}$  will be satisfied only when 

• A

  the galvanometer shows a deflection when switch S is closed

• B

  the galvanometer shows a deflection when switch S is open

• C

  the galvanometer shows no change in deflection whether S is open or closed

• D

  the galvanometer shows no deflection