You arrive on the scene and find an elderly male complaining of severe abdominal and back pain. Upon further questioning, he states that the pain is "all over the left side." On palpation, you feel a pulsating mass in the abdomen. From which of the following is this patient most likely suffering?

A. pulsating diaphragm lesions
B. acute arterial occlusion
C. acute pulmonary embolism
D. abdominal aortic aneurysm