Robbery Is a Face-To-Face Confrontation Between the Victim and Perpetrator

Robbery is a face-to-face confrontation between the victim and perpetrator.Why is it that many times witnesses are unable to provide much descriptive info about the perpetrator?

A) The perpetrator wore a mask of some type.
B) The witnesses are able to provide information about the suspect.
C) Witnesses are often upset and may have seen the perpetrator only briefly.
D) The witnesses observe the perpetrator but are reluctant to describe him/her for fear of reprisals.