Margo was frightened and confused when a robber appeared at the convenience store where she works. it seemed that the only thing she could see was the gun he had pointed right in her face. later, when margo serves as an eyewitness, she may not be reliable because of problems she had at the stage of memory processing.

The correct answer should be acquisition.
She had problems in the pre-stage of memory processing, which is the acquisition of the memory itself. She failed to create, or acquire a particular memory because she didn't pay attention to the robber, but rather only to his gun. Therefore she isn't really reliable as an eyewitness given that she didn't actually 'see' the robber.