Three Originally Uncharged Infinite Parallel Planes Are Arranged as Shown

Three originally uncharged infinite parallel planes are arranged as shown.Then the upper plate has surface charge density σ placed on it while the lower plate receives surface charge density −σ.The net charge induced on the center plate is

A) 0.
B) −σ/2.
C) +σ/2.
D) −σ.
E) +σ.