A, because the crown block is in a state of balance, the upward force of the crown block is the pulling force of rope B, and the downward force is the downward pulling force of gravity rope A on the crown block, so the pulling force of rope B on the crown block is unbalanced with gravity, so option A is wrong;

B. Because the upward pull of rope A on the weight and the downward pull of the weight on rope A are a pair of interaction forces, option B is wrong;

C, because the weight is in a state of balance, and the object is only subjected to downward gravity and upward pull of the rope A on the weight, so the upward pull of the rope A on the weight and the gravity of the weight are a pair of balancing forces, so option C is correct;

D, because the downward pull of heavy objects on the rope A and the downward pull of people on the rope do not act on an object, which is not a balancing force, option D is wrong.

So choose C.