Who are the individuals acting within the scope of their authority that can modify or change contracts on behalf of the Government?

The correct choice is the Contracting Officer because they hold the designated authority to negotiate, enter into, and amend contracts on behalf of the Government. Their role is integral in ensuring that all modifications adhere to legal and regulatory frameworks. The Contracting Officer's authority is established through specific training, certification, and delegation of powers under federal acquisition regulations.

While contracting agents may assist in the process and project managers may have significant input regarding contract execution, they do not inherently possess the authority to modify contracts. Department heads may oversee budgets and project alignment but their role does not typically extend to altering contract terms. The distinct authority and responsibility of the Contracting Officer ultimately ensure accountability and compliance in the contract modification process, which is crucial in government contracting.