What Creates the Electrical Charges in Clouds That Characterize Lightning

What creates the electrical charges in clouds that characterize lightning storms?

A) friction between air molecules in turbulent air in the clouds
B) friction between droplets of water falling in clouds and others carried upward in updrafts
C) natural charges on the Earth's surface repel equally charged surface charges on droplets in the cloud base
D) collisions between ice particles rising and falling in turbulent air in the clouds
E) collisions between falling ice particles and water droplets carried in updrafts