Answered

Min tapes a piece of string to each of two ping-pong balls. He hangs the balls so that they are close to one another but do not touch. Later, he finds that they have pulled together. They are now touching. What could explain why two balls are now touching?

Athey have both lost their charges

Bthey have gained opposite charges

Cthey have both gained a positive charge

Dthey have both gained a negative charge