Kat is a middle-school teacher who survived a mass shooting at her school 3 weeks ago that claimed the lives not only of several of her colleagues but of three of her fifth-grade students. She remembers very little of the event. Kat’s lack of memory is an example of a(n) symptom of acute stress disorder.

The correct answer is - dissociative.

Explanation:

Acute stress disorder is a mental condition that is characterized by the increasing development of a serious dissociation, anxiety and many other symptoms such as depression, behavioral change and many other that takes place after a traumatic incident such as death, accident or similar cases.

In this case Kat is exhibiting dissociation symptom of the acute stress disorder as she is not remembering her colleagues and students after very little of the mass shooting at her school.

Thus, the correct answer is - dissociative.