The answer is most likely D- all of these are correct. If you are talking about explorers like Christopher Columbus and any other 15th and 16th century European explorers, all of these obstacles apply. Many explorers were finding new trade routes to India and other countries, which made them face the fear of the unknown. Disease and starvation were also common when a new continent was discovered (North America). In these centuries, many explorers had poor maps and navigational tools because the technological advancements that occurred in the later ages hadn't developed yet.