Joel inflates a balloon and ties it off. He then rubs the balloon against his hair, which makes his
hair stand up. He then places the balloon near the classroom wall and sticks it to the wall. Finally, he
pops the balloon with a pin. Which of these is an example of gaining a charge by friction in this example?

A. Rubbing the balloon against his hair
B. Placing the balloon near the classroom wall
C. Touching the balloon to the classroom wall
D. Popping the balloon with a pin