The correct answer is: a) Nongpok Keithelmanbi.
Nongpok Keithelmanbi is a village in Imphal West district of Manipur, India. It is located about 10 kilometers from Imphal, the state capital. The village is known for its archaeological site, which has yielded evidence of prehistoric human habitation. The site has been excavated by the Archaeological Survey of India, and has yielded a number of stone tools and pottery. The tools are made of chert and quartz, and are of the Neolithic period. The pottery is of the Chalcolithic period. The site is significant because it provides evidence of the earliest human habitation in Manipur.
The other options are incorrect because they are not archaeological sites in Manipur. Kangla is a historical fort in Imphal, and Khangkhui Cave is a cave in Senapati district. Sekta is a village in Imphal East district.