The correct answer is: b) Kannauj.
Harshavardhana was an Indian emperor who ruled over the northern Indian subcontinent in the 7th century CE. He was the founder of the Harsha Empire, which at its peak extended from Bengal in the east to Punjab in the west, and from Kashmir in the north to the Narmada River in the south.
Harshavardhana’s capital was located at Kannauj, which is now a city in the Indian state of Uttar Pradesh. Kannauj was an important center of trade and culture during Harshavardhana’s reign. It was also the site of several important temples and monasteries.
The other options are incorrect. Pataliputra was the capital of the Mauryan Empire, which was a different empire that ruled over northern India centuries before Harshavardhana. Ujjain was an important city during the Gupta Empire, which was another different empire that ruled over northern India centuries before Harshavardhana. Thanjavur was an important city during the Chola Empire, which was a different empire that ruled over southern India centuries after Harshavardhana.