Final answer:
The aorta is the structure that cuts through the diaphragm at T12 level, transitioning into the abdominal aorta through the aortic hiatus.
Step-by-step explanation:
The structure that cuts through the diaphragm at the level of T12 is the aorta. When passing through the diaphragm, the aorta transitions into the abdominal aorta and does so through an opening known as the aortic hiatus. Additionally, the thoracic duct and azygous vein also pass through this hiatus in the posterior diaphragm. It is important to note that other structures pass through the diaphragm at other levels, such as the inferior vena cava through the caval opening and the esophagus through the esophageal hiatus.