If employees are required to handle or use ___, they shall be trained regarding the safe handling and use of these.

The correct answer is rooted in the need for safety training when employees are required to handle hazardous materials. Both poisons and caustics can pose significant health risks if not handled properly.

Training regarding safe handling and use is essential, as it equips employees with knowledge about potential hazards, appropriate safety equipment, and procedures to mitigate risks involved in working with these substances. This training not only helps in protecting the health and safety of the workers but also ensures compliance with workplace safety regulations.

Since both materials are categorized as hazardous, including either one within the requirement for training emphasizes the importance of safety protocols in the workplace. Consequently, the inclusion of both options as valid answers underlines the essential nature of training for handling dangerous substances.