Darin had an automobile accident in which his brother and another passenger were killed. though darin wasn't seriously hurt in the accident, he can't remember any of the accident details. darin is engaging in which ego defense mechanism?

Darin is going through repression.  Repression is what happens after a traumatic event happens, and it's a psychological defense mechanism where the brain tries to just remove something from the memory of the person affected.  Basically, it's the brain pushing all these bad memories into a box and locking up the box and not letting the memories out.  

Look at some up some videos about like eureka math or khan Academy