What safety measure should be taken when working on circuits?

Using insulated tools is an essential safety measure when working on circuits because these tools are designed to prevent electrical shock. Insulated tools have rubber or non-conductive coatings that provide a barrier against electrical current, ensuring that even if the tools come into contact with a live circuit, the user is protected. This is especially critical when working on high-voltage systems or in environments where the risk of electrical contact is increased.

The other choices do not meet the safety standards required for working on electrical circuits. Wearing rubber gloves can be beneficial, but without using insulated tools, you still risk encountering electrical hazards. Ensuring that the circuit is live would be dangerous, as it increases the chance of electrical shock, and using metallic tools could lead to a direct short circuit or electric shock if they make contact with live wires. Thus, the emphasis on insulated tools as a primary safety measure ensures greater protection for those working in electrical environments.