A non-conducting sphere of radius R=3 cm caries a charge of Q=2uc distributed uniformly throughout its volume. At what distance, measured from the center or the sphere, does the electric field reach a value equal to half its maximum value?
a). 4.2 cm only B) 2.1 cm only C) 1.5 cm only D) 1.5 cm and 2.1 cm E) 1.5 cm and 4.2 cm