13. The plates of a parallel-plate capacitor of capacitance C₀ are horizontal. Into the gap a slab of dielectric material with κ = 2 is placed, filling the bottom half of the gap between the plates. What is the resulting new capacitance? (A) 2/5 C₀ (B) 3/4 C₀ (C) 2 C₀ (D) 5/2 C₀ (E) 4/3 C₀