When configuring a newMetric Definitionto track theduration an incident is assigned to a specific group,...

To track how long an incident remains assigned to a specific group, the correct Metric Definition type isField value duration. This type measures the amount of time a record spends with a particular value in a specified field, such as assignment_group.

State change metrics track transitions between states, not time spent in a field value. Script calculations are used only when duration cannot be calculated through standard field tracking. “Assignment group” is a field, not a metric type. ServiceNow documentation specifies that Field value duration metrics are designed for tracking time spent in a given field value, making option A the correct choice.