19. A proton with speed  v = 3.00×105m/s orbits just outside a charged sphere. The radius of the orbit is 1.0 cm. What is thecharge on the sphere? (The mass of a proton is 1.67×10−27kg.)
(A)1.04×10−9C 
(B)3.47×10^{−8C 
(C)6.23×10−8C 
(D)6.50×10−8C 
(E)8.28×10−7C}