A Vacuum Dielectric, Parallel-Plate Capacitor Has a Potential Across the Plates

Multiple Choice

A vacuum dielectric, parallel-plate capacitor has a potential across the plates of 13.3 V and a plate separation distance of 1.1 mm. A polystyrene dielectric, $x = 2.5$ , is inserted between the plates (the potential remains constant) . The electric field between the plates is now

A) 30,000 N/C.
B) 15,000 N/C.
C) 4800 N/C.
D) 2100 N/C.