Which city-state was the last to surrender to shih huangdi before the unification?
a: the state of qi
b: the state of zhao
c: the state of han
d: the state of yan

Qin's wars of unification were a series of military campaigns launched in the late 3rd century BC by the Qin state against the other six major states — Han, Zhao, Yan, Wei, Chu and Qi — within the territories that formed modern China. By the end of the wars in 221 BC, Qin had unified most of the states and occupied some lands south of the Yangtze River. The territories conquered by Qin served as the foundation of the Qin dynasty. so the state of Qin