21. The hollow metal sphere shown above is positively charged. Point C is the center of the sphere and point P is any other point within the sphere. Which of the following is true of the electric field at these points?
(A) It is zero at both points.
(B) It is zero at C , but at P it is not zero and is directed inward.
(C) It is zero at C , but at P it is not zero and is directed outward.
(D) It is not zero at either point.