A nail _____ be used as an appropriate handle tie for two breakers.

The correct choice emphasizes that a nail should not be used as a handle tie for two breakers due to safety and code compliance considerations. In electrical installations, a handle tie is a mechanism that ensures two circuit breakers operate together or can be turned off simultaneously, usually for safety when working on multi-phase circuits.

Using a nail as a handle tie would not provide the necessary stability or security required for proper function. It could lead to hazardous conditions, such as the breakers not being properly disconnected, which may result in electrical shock or fire hazards. Regulatory standards typically specify approved materials and methods for electrical work to ensure safety and integrity, which a nail does not fulfill. Thus, indicating that a nail must not be used aligns with best practices for electrical safety.