A Metallic Sheet Has a Large Number of Parallel Slits,5

A metallic sheet has a large number of parallel slits,5.0 mm wide and 20 cm apart.This sheet is used as a grating for microwaves.A wide parallel beam of microwaves is incident normally on the sheet.What is the smallest microwave frequency for which only the central maximum will occur? (c = 3.00 × 10⁸ m/s)

A) 0.50 GHz
B) 0.70 GHz
C) 1.0 GHz
D) 1.5 GHz
E) 2.0 GHz