Which of the following best describes the contractor's ability to perform extra work?

The correct answer emphasizes that contractors are permitted to perform extra work only after receiving official modifications. This is crucial because it establishes a formal process that ensures any additional work is documented, approved, and aligned with the contractual obligations. Official modifications protect both the contractor and the client by clearly outlining the scope, terms, and potential adjustments in payment or project timeline.

Other choices misunderstand the essential governance of contractual agreements. Allowing performance without needing approval would lead to confusion and potential disputes regarding compensation and responsibilities. Claiming that additional work is always permissible under any circumstances undermines the structure of contracting, which requires accountability and management of changes. Stating that no additional work can ever be performed ignores the practical need for flexibility in adapting to evolving project requirements.