Which defense mechanism is illustrated by a trauma victim who cannot recall the events leading to the accident?

The patient is a trauma victim who "cannot recall the events leading to the accident." This indicates an involuntary and unconscious forgetting of distressing or traumatic memories.

• A. Repression: An unconscious defense mechanism where unacceptable thoughts, feelings, or memories are pushed out of conscious awareness to protect the ego from anxiety. The individual genuinely cannot recall the information.
• B. Denial: A defense mechanism where an individual refuses to accept reality or facts, often to avoid a painful truth. The person is aware of the reality but denies its existence or implications.
• C. Displacement: A defense mechanism where a person redirects an emotional reaction from the original, more threatening source to a safer, substitute target.
• D. Suppression: A conscious defense mechanism where an individual intentionally pushes unwanted thoughts, feelings, or memories out of awareness. The person is aware of the memory but chooses not to think about it.

The inability to recall traumatic events, especially when it's involuntary ("cannot recall"), is characteristic of repression, an unconscious process where the mind protects itself from overwhelming distress by burying the memory. Suppression involves a conscious effort, while denial involves refusing to acknowledge something that is known.

The final answer is $\boxed{\text{A. Repression}}$