听力原文：Hi, everyone, as we mark the anniversary of the Iraq war, we're being reminded of all that our soldiers have sacrificed and what some continue to experience. The scandal of Walter Reed put their suffering into sharp focus and so was a new study from the Archives of Internal Medicine. The study found that about a third of returning vets were diagnosed with mental illness, or a psychosocial disorder, everything from depression and post-traumatic stress to homelessness and domestic violence. The highest rate of mental problems is among the youngest- soldiers between 18 and 24. The doctor who conducted this study says the numbers may eventually surpass those from Vietnam. According to the passage, the highest rate of mental problems is not in the age of ______.