$2.$ The local two$-$phase mass transfer coefficient for a gas$-$liquid system depends on the $\_\_\_$ of the gas phase, the $\_$ of the liquid phase, and the $\_\_\_$ at the interface.

$-$ a$)$ viscosity, density, turbulence

$-$ b$)$ density, temperature, pressure

$-$ c$)$ temperature, viscosity, concentration gradient

$-$ d$)$ pressure, flow rate, surface tension