The I-V characteristics of a p-n junction diode in forward bias is shown in the figure. The ratio of dynamic resistance, corresponding to forward bias voltage of \( 2 \, \text{V} \) and \( 4 \, \text{V} \) respectively, is:
\( 1 : 2 \)
\( 5 : 1 \)
\( 1 : 40 \)
\( 20 : 1 \)