What was the main reason for the isolation of japan?
a. weak rulers
b. lack of education
c. domination by chinese culture
d. difficult navigation in surrounding seas

These answers seem to be somewhat strange. None of these answers could be really considered correct. Japan  has always been a very self-sufficient country that has relied on itself. Later on during an era when isolation was an active strategy of the Japanese people it was done due to a desire of minimizing foreign influence. Among these D - difficult navigation in surrounding seas would perhaps be most correct. 

The answer is on suffrage experience.