What is a question about this article? If the question is unanswerable, say "unanswerable".

Being one of the four ancient capitals of China, Nanjing has always been a cultural centre attracting intellectuals from all over the country. In the Tang and Song dynasties, Nanjing was a place where poets gathered and composed poems reminiscent of its luxurious past; during the Ming and Qing dynasties, the city was the official imperial examination centre (Jiangnan Examination Hall) for the Jiangnan region, again acting as a hub where different thoughts and opinions converged and thrived.

When did the city serve as the official imperial examination centre?
the Ming and Qing dynasties