There are N boxes, each containing at most r balls. If the number of boxes containing at least i balls is $N_{i}$ for i = 1,2,...r, then the total number of balls contained in these N boxes

(A) is exactly equal to $N_{1}$ +$N_{2}$ +...+$N_{r}$.

(B) is strictly larger than $N_{1}$ +$N_{2}$ +...+$N_{r}$.

(C) is strictly smaller than $N_{1}$ +$N_{2}$ +...+$N_{r}$.

(D) cannot be determined from the given information