A single point charge of +q is placed at the very center of two spherical shells. The inner shell is non-conducting, has a charge of -2q, and an inner radius of a and outer radius of b. The outer shell is a conductor and has an inner radius of b and an outer radius of c. What is the electric field at r?:
a) r < a
b) a < r < b
c) b < r < c
d) c < r