Brainlest for the answer! What was an effect of the Mongol invasions during the Kamakura shogunate?

a The invasions were costly to defend against, and they created financial problems.
b The invasions strengthened the economy because people spent money to prepare for war.
c The Mongols won and oversaw a new period of peace that lasted nearly three hundred years.
d The Mongols overthrew the shogunate and brought an end to the feudal system.