One purpose of a structure is to provide access to underground pipes for runoff and:

• A. Water
• B. People
• C. Gases
• D. Animals

Answer: (B)

The main idea is that these underground access structures exist so people can reach the pipes for maintenance and inspection. Structures like manholes let maintenance crews enter the sewer or storm drain to inspect, clean, and repair the lines without wide-scale excavation. Water is what the pipes carry, but the reason for the access point is not to provide water. Gases or animals might be encountered, but ventilation or animal access aren’t the primary design purpose of these structures. So, the best answer is that the purpose is to provide access for people to maintain the runoff system.