At the ligamentum arteriosum-the ligamentum arteriosum is the point where the left pulmonary artery connects with the undersurface of aortic arch. it is a remnant of the fetal ductus arteriosus, which shunted blood away from the developing lungs. because the aorta is tethered to the pulmonary artery by the ligamentum arteriosum, the part of the aorta near the ligamentum is vulnerable to damage in a traumatic acceleration/deceleration injury - it could pull away and tear. the other answer choices do not describe points of the aorta where a mobile and fixed portion meet. therefore, these parts of the aorta would not be vulnerable to this type of traumatic injury.