John agrees to supply Sarah with goods from a foreign country. When the government in that country is overthrown in a violent revolution, it becomes impossible to obtain the goods except at a much higher price. This outcome will

a.) constitute a breach of the agreement because John can no longer supply Sarah with the goods at the agreed price

b.) not constitute a breach of the agreement since the possibility of violent revolution is not the type of risk ordinarily assumed in business

c.) not constitute a breach of the agreement because a violent revolution would probably be characterized as an unforeseen difficulty

d.) both b and c