Answer:
B
Step-by-step explanation:
The reason why sentence B suggests that Bamburgh is one of the oldest castles in England is that it specifically mentions that Ida, an early English warlord, founded his kingdom in 547 CE and built the castle Bamburgh. By stating that the castle was built by Ida in the early English kingdom, it implies that Bamburgh has a long history and is one of the oldest castles in England.