$(a)\;\frac{\Delta V_{BE}}{\Delta I_c} \\ (b)\;\frac{\Delta R_{BE}}{\Delta I_c} \\ (c)\;\frac{\Delta I_c}{\Delta I_B} \\ (d)\;\frac{\Delta I_c}{\Delta v_{BE}} $

where

$\Delta V_{BE} $ -Potential difference across base emitter

$\Delta I_C$- charge in collector current

$\Delta I_B$- change in base current

$\Delta R_{BE} $ change in base- emitter resistance