Which of the following is a valid long-distance dialing format?

The selected answer is correct because it adheres to the standard long-distance dialing format used in North America. In this format, the process begins with the digit '1,' which indicates that the call is a long-distance call. Following this, the area code is included to specify the region of the number being dialed, and then the seven-digit local number completes the format.

This structure is essential for correctly routing long-distance calls within the telecommunications system, ensuring that each element is clearly recognized to facilitate connection to the intended recipient.

The other options presented do not conform to the standard long-distance dialing format. For example, using '0' at the beginning followed by an area code signifies a different type of dialing method, typically used for operator services rather than standard long-distance calls. Furthermore, dialing '411' signifies directory assistance rather than a specific local number, which illustrates its inapplicability in this context. Thus, the choice of '1 + area code + seven-digit number' is the only valid long-distance dialing format.