Explanation

(c) Amplification factor,
$\mu = \frac{\mathrm{\Delta}V_{p}}{\mathrm{\Delta}V_{g}} = \frac{\mathrm{\Delta}V_{p}}{\mathrm{\Delta}V_{g}} \times \frac{\mathrm{\Delta}I_{p}}{\mathrm{\Delta}I_{p}} \times \frac{\mathrm{\Delta}I_{p}/\mathrm{\Delta}V_{g}}{\mathrm{\Delta}V_{p}/\mathrm{\Delta}V_{p}}$
$= \frac{slope\ of\ naode\ characteristies}{slope\ of\ mutual\ charactristies}$