Due to decelerations, aoa can be ruptured at places where it is fixed except:

Ans is 'b' i.e. Behind the esophagus "The majority of blunt injuries to the thoracic aoa occur at aoic isthmus just distal to the left subclan aery. Other locations include the transverse arch, proximal ascending aoa, and descending aoa just proximal to the diaphragm." - Sevitt S. The mechanisms of traumatic rupture of the thoracic aoa. Br J Surg 1977; 64:166 About 'aoic valves' the following reputed radiologly website writes: "The above figures represent the site of injury in those patients who present to hospital. The ascending aoa is injured in 20 to 25% of cases at autopsy but most of these patients die at the scene from serious complications such as a ruptured aoic valve, coronary aery laceration or haemopericardium with pericardial tamponade." Aoic isthmus is poion of the proximal descending thoracic aoa between the left subclan aery origin and the ligamentum aeriosum. Tethering of the aoa by the ligamentum aeriosum is believed to account for the high frequency of aoic injury in the isthmus region. The isthmus is thought to be a transition zone between the more mobile ascending aoa and arch and the relatively fixed descending thoracic aoa which allows for stretching with rapid deceleration