Three pith balls supported by insulating threads hang from a support. We know that ball X is positively charged. When ball X is brought near balls Y and Z without touching them, it attracts Y and repels Z. Since pith is an insulating material, we can conclude that:

A. Y has a negative charge.
B. Z has a negative charge.
C. Y has a positive charge.
D. Z is neutral (has no net charge).
E. Y is negatively charged or neutral (has no net charge).