A Solid Sphere of Radius a Is Concentric with a Hollow

Multiple Choice

A solid sphere of radius a is concentric with a hollow sphere of radius b, where b > a. If the solid sphere has a uniform charge distribution totaling +Q and the hollow sphere a charge of -Q, the electric field at radius r, where r < a, is which of the following, in terms of k = (4 $\pi$$\isin$ ₀) ^-1?

A) kQ/r²
B) kQr/a³
C) kQ/a²
D) kQ/b²
E) zero