Which of the following should never be flushed into a septic system?

The choice that states chemicals, oils, and non-biodegradable items is correct because these substances can severely harm the septic system's functionality. Septic systems are designed to process organic waste and rely heavily on bacteria and enzymes to break down waste materials. When harmful chemicals, oils, and non-biodegradable items are introduced, they can disrupt the balance of beneficial bacteria necessary for waste decomposition. Chemicals can be toxic to these organisms, leading to system failure, while non-biodegradable items can clog the system and prevent proper drainage and treatment of waste. This highlights the importance of maintaining the integrity of a septic system by being mindful of what is flushed or disposed of.