Answer: D

Reasoning: Swallowed blood, intra-operative nitrous oxide and peri-/post-operative opioid use are well-established emetogenic factors that increase the risk of postoperative nausea and vomiting. In contrast, acetaminophen is not an emetogen and, when given intravenously, has actually been shown to lower PONV rates compared with placebo [Apfel 2013, PMID 23433945].