I believe it's C. Zhu Yuanzhang hope it's right :)
Japan has many mountains, thus, the outsiders could not easily enter Japan and Japanese could not leave the country. And, thus the self-isolation was helped by the presence of a mountain terrain. This policy was implemented by Togukawa, who insisted on preventing Japan from foreigners.
Is there any answers to choose from? if not i would say a debit card.
