Which dynasty ruled over Kannauj in the medieval period in India?

Kannauj, located in the Ganga-Yamuna doab, was the most contested political prize of early medieval northern India between the eighth and eleventh centuries CE. Three major powers, the Gurjara-Pratiharas, the Palas, and the Rashtrakutas, fought for control of the city in what historians call the Tripartite Struggle, because whoever held Kannauj controlled the wealth and trade routes of the Gangetic plain.

The city changed hands more than once across the wider medieval period: the Pala ruler Dharmapala briefly installed a client ruler at Kannauj before losing it, and centuries later the Gahadavala dynasty held the city from around 1090 to 1194 CE. This question is understood in its standard, exam-convention sense: which dynasty held Kannauj as its own imperial capital during the classic Tripartite Struggle. In that established sense, the Gurjara-Pratiharas are the dynasty credited with ruling Kannauj.

The Gurjara-Pratihara ruler Nagabhata II captured Kannauj from Pala control around 815-816 CE and made it his empire's capital. Under his successors Mihira Bhoja and Mahendrapala I, the Pratihara empire expanded across much of northern India from this base, and Kannauj remained the Pratihara capital for roughly two centuries, until Mahmud of Ghazni's raid in 1018 CE forced the ruler Rajyapala to abandon the city; the dynasty continued afterward in a much reduced form away from Kannauj.

Among the dynasties named in the options, only the Gurjara-Pratiharas held Kannauj as their imperial seat during the medieval period, which is why Gurjar Pratihars is the correct answer.