Which of the following is an example of a geographic barrier?

The correct answer highlights that mountains and oceans are significant examples of geographic barriers. Geographic barriers are natural features that impede movement and interaction between different areas. Mountains create physical obstacles that can limit travel and influence the development of cultures and communities on either side. Similarly, oceans serve as vast bodies of water that can hinder transportation and communication, especially in historical contexts where technology did not allow for easy crossing.

While deserts and forests, as mentioned in the other options, can serve as barriers to some extent, they do not have the same widespread impact as mountains and oceans in terms of defining and shaping human geography. Deserts can limit settlement due to their arid conditions, and forests can restrict movement through dense vegetation, but they are often more navigable than towering mountains or wide oceans. Rivers and valleys also present barriers, but they can be both facilitating travel and navigation as well, depending on the context. Therefore, mountains and oceans stand out as the most significant geographic barriers due to their size and the challenges they present for movement and interaction.