The correct answer is - b. We have to be prepared for raids from ferocious invaders from Scandinavia.
The people living on the western coast of Europe, during the Medieval period, were living in constant fear for few hundred years because of the raids that were constantly happening by the invaders from Scandinavia, commonly known as Vikings. The Vikings were well known for being big, strong, ferocious, excellently trained military force, that was coming from the sea unexpectedly. They were robbing, raping, taking slaves, and very often capturing places that were suitable as ports, as they were primarily a naval force that was mostly focused on the sea trade.
