The correct answer is B. Add the user to the local Administrators group, because this provides the necessary permissions to install software on a specific machine without granting excessive privileges across the entire domain. This approach follows the principle of least privilege while still allowing the user to perform required testing tasks.

According to the Quentin Docter – CompTIA A+ Complete Study Guide, local administrator rights allow users to install and configure applications on a single system but do not grant access to domain-wide resources. This makes it an appropriate choice for sandboxed or test environments.

The Travis Everett & Andrew Hutz – All-in-One Exam Guide warns against adding users to the Domain Admins group, as this grants full control over the entire Active Directory environment and poses a significant security risk. Sharing credentials or passwords violates security best practices and audit requirements.

The Mike Meyers / Mark Soper Lab Manual reinforces that granting local administrative access is a common and accepted practice in controlled testing scenarios, especially when systems are isolated from production environments.

Because the goal is to allow software installation without compromising domain security, adding the user to the local Administrators group is the best and safest option, making B the correct answer.