Which of the Following Made the Atlantic and Pacific Oceans

Which of the following made the Atlantic and Pacific Oceans difficult to traverse until relatively recently in human history?

A) their great size compared to other waterways
B) a lack of interest on the part of earlier human civilizations to make the journey
C) the inability of early human civilizations to track and record weather patterns
D) the lack of ships capable of traversing the Atlantic and Pacific until the eighteenth century C.E.