Which of the following are physical methods to prevent or reduce the quantity of liquid flowing into the environment?

All of the options listed—dikes, dams, diversion, and retention—are effective physical methods used to prevent or reduce the flow of liquids into the environment.

Dikes are barriers constructed to hold back water and can be crucial in protecting specific areas from floodwaters, thereby minimizing the risk of contamination from hazardous liquids. Dams serve a similar purpose by controlling water flow and creating reservoirs that can store excess liquid, preventing spillage into surrounding areas.

Diversion methods involve redirecting the flow of liquid away from sensitive areas, thus preventing potential runoff or contamination. Retention systems are designed to contain liquid materials, often holding them in designated areas to control their release into the environment effectively.

By utilizing all these methods collectively, an integrated approach is taken to manage liquid containment and minimize environmental risks. Each method supports the overall goal of environmental protection, making the comprehensive answer of "All of the above" the most appropriate choice.