The writer's mother, it seems, _______.

A．the tops of thunderclouds have a great positive charge
B．the bottoms of the clouds have a great negative charge
C．only the middles of thunders are electrically charged
D．both A and B

A．Positive charges are in the top of the cloud, negative charges in the bottom.
B．When positive and negative charges within a cloud cannot break down the insulating properties of air, no lightening will be formed.
C．Without hail and thunder, there could be no lightening.
D．Without refrigerated rods, lightening could not be created.