$A$ coil having $n$ turns and resistance $R \, \Omega$ is connected with a galvanometer of resistance $4 \, R \, \Omega$. This combination is moved in time $t$ seconds from a magnetic field $W_1$ weber to $W_2$ weber. The induced current in the circuit is

• A
  $ - \frac{W_2 - W_1}{5 R n t}$
• B
  $ - \frac{n(W_2 - W_1)}{5 R t}$
• C
  $ - \frac{W_2 - W_1}{R n t}$
• D
  $ - \frac{n(W_2 - W_1)}{R t}$