Gene Is a Child Who Recently Immigrated to Canada from a War-Torn

Gene is a child who recently immigrated to Canada from a war-torn country where he lived in several refugee camps. Before arriving in Canada, he witnessed many atrocities and was frequently worried about his safety and the safety of his family. After immigrating, he was constantly anxious during school and suffered from frequent nightmares. A school psychologist would most likely conclude that Gene has:

A) agoraphobia.
B) generalized anxiety disorder.
C) panic disorder.
D) post-traumatic stress disorder.