Final answer:
The structure that cuts through the diaphragm at T8 is the inferior vena cava, which passes through the caval opening according to the information provided.
Step-by-step explanation:
The question asks which structure cuts through the diaphragm at the level of the thoracic vertebra T8. According to the provided passages, the three main openings present in the diaphragm are for the inferior vena cava, which passes through the caval opening, the esophagus, which passes through the esophageal hiatus, and the aorta, the thoracic duct, and the azygous vein which pass through the aortic hiatus. Given these options and the information that the inferior vena cava passes through the diaphragm at T8 (part of the mnemonic IKEA), the correct answer is A. Inferior vena cava.