Which of the following is a condition where an employee's injury would be excluded from compensation?

The correct choice identifies conditions under which an employee's injury would not qualify for compensation. Specifically, injuries from participating in off-duty recreational activities are typically excluded from workers' compensation. This is because these activities occur outside the scope of employment and are not related to the job duties or responsibilities.

In contrast, injuries resulting from workplace accidents, those sustained during mandatory training sessions, and injuries occurring during work-related lunches are generally considered compensable, as these situations are directly linked to the employee's work obligations.

By understanding that off-duty recreational activities do not involve the employer's direct interest or control, it's clearer why injuries from these activities fall outside the boundaries of compensable workplace injuries. Hence, option C aptly illustrates a scenario where compensation would typically be denied.