The best answer to the question "Why do some people struggle with water scarcity?" is:
A. Freshwater resources are not evenly distributed across the Earth’s surface.
This statement accurately reflects the geographic and political factors that contribute to water scarcity, as some regions have abundant freshwater resources while others do not. The other options, while they may relate to broader issues regarding water and the environment, do not directly address the primary reason for water scarcity experienced by some populations.