The Ming dynasty lasts for ____ years. Its rulers live in the ____, a vast palatial compound. No one can enter or leave without the emperor's _____. It takes up to a million workers _____ years to build.

a) 300, Imperial City, permission, 50
b) 500, Forbidden City, consent, 100
c) 700, Grand Palace, approval, 200
d) 1000, Emperor's Citadel, authorization, 500