Which of the Following Pr°Cesses Can Generate the Convective Instability

Which of the following pr°Cesses can generate the convective instability ass°Ciated with severe thunderstorms and tornadoes?

A) forcing a layer of moist air to descend a mountain range
B) creating shadows on the land surface
C) heating the upper portion of an unsaturated layer of air
D) lifting a stable air layer whose surface is humid and whose top is dry