Question

object a is positively charged.
objects a and b attract each other.
objects b and c repel each other.
the charge on b is select.
the charge on c is select.

Explanation:

1. For object B: A positively charged object attracts objects that are negatively charged (opposite charges attract) or neutral (induced charge). But since B repels C, B cannot be neutral (neutral objects don't repel anything), so B must be negatively charged.
2. For object C: Like charges repel, so since B is negatively charged and repels C, C must also be negatively charged.

Answer:

The charge on B is negatively charged
The charge on C is negatively charged